LITERATURE REVIEW
Introduction
Bicycling is one of the most sustainable modes of transport and plays an important role in the transport system. Cycling has a number of benefits that include improving the quality of life, reduction of traffic congestion in cities, positive health outcomes due to the exercises involved, providing a suitable form of transport for short distances and environmental conservation among many other benefits. A number of cities have adopted bicycle master plans as they try to capitalize on the cycling opportunity (Litman et al., 2005). This has meant that bicycle ways are being created and existing roads are being redesigned to cater for cyclists. In trying to identify and build bicycle pathways, a number of factors are being considered including topography. A number of researchers have studied cycling trends and cyclist behavior and have found out that the slope gradient, travel time, travel cost, travel time, length and speed are factors that affect cycling as the result in travel impedance. Research studies have revealed that bicyclists are more sensitive to topography and the slope. Slopes, especially steep slopes cause travel impedance. A number of researchers have come up with methods for slope-based bike segmentation such as Huang & Ye (1995). A number of methods to assess path segmentation difficulty due to slope have been developed and include their assessment based on their age, skill and comfort level (AASHTO, 2012). Some methods base on rider frequency while others on level of proficiency. With the advent of GIS technologies, it has become increasingly possible to map and plan for cycling routes, locating areas, determining the longest and shortest routes for cycling and map out hazards along the routes that may affect cyclists.
Importance of Bike Riding
Cycling has a large number of benefits as compared to the motorized forms of transportation of passengers. The benefits of cycling can be categorized into the health benefits, social benefits, economic and environmental and sustainability benefits. The first benefit of cycling relates to the easing of traffic congestion. Cycling greatly reduces the over-reliance on private cars and public transport (Teshome, 2006). Traffic congestion is a major issue in most urban areas and results in reduced productivity among the workers. As compared to the other forms of transport, cycling causes minimal congestion. Secondly, cycling has a wide range of health benefits. Among many cyclist, their motivation stems from health related reasons. Since it’s a physical activity, cycling translates to disease prevention and contributes to better public health outcomes (Winters, 2011; Teshome, 2006).
Additionally, cycling results in fewer emissions that cause pollution and fewer accidents as compared to the motorized transport (Fraser, SD & Lock, 2010). Cycling reduces air pollution and results in the prevention of diseases such as heart attacks and obesity (Fraser, SD & Lock, 2010; Teshome, 2006). Cycling has a number of environmental benefits given that it is energy efficient, does not cause any air pollution and does not result in greenhouse gas emissions. Cycling greatly contributes to the mitigation of climate change which is a problematic issue in the world today. Due to the fact that it does not emit greenhouse gases, it ensures the protection of the earth. Cycling also provides a number of social benefits that include improving the social well-being of the community, provision of social capital and encouragement in community participation in issues (Teshome, 2006). Cycling is relatively cheap hence saving people the high transportation costs. It also provides a comfortable and fast mode of transport for the short journeys (Teshome, 2006). Some of the benefits are listed in the Fig below.
Source: Litman et al., (2005)
Factors Affecting Bike Riding
Impact of Slope Gradient
A huge body of literature reveals that there exist a number of factors that are relevant when addressing the impact of slope to bicycle riders and the suitable routes riders choose. For instance, factors such as the design of the street network, diversity establishments and the various land uses have a direct influence on the physical distance that cyclists have to cover from their points of origin to their potential destinations. Fraser & Lock (2010) found out that a number of unfavorable conditions found in terrain such as a steep slope, weather, traffic conditions, street connectivity, street density and the density of the road have a negative impact on the cyclists. For example, due to these conditions, the cyclists will be required to use more effort when they travel from one destination to another, which leads to an increase in travel impedance (Fraser & Lock 2010; Wardman, Parkins, & Page 2008). Besides, the presence of well-planned and improved facilities such as bike lanes, off-road bike trails, paths and sidewalks ensures a more comfortable ride for the cyclists. It has been found out that many bicycle riders are usually sensitive to the topography and will most likely avoid slopes that are steep and opt for the gradual and gentle slopes (Wardman, Parkins, & Page 2008). Many of the riders strive to use minimal human energy and reduce travel impedance (Wardman, Parkins, & Page 2008).
In a study conducted by Wardman, Parkins & Page (2008) in the UK, the researchers established that a slope variable was more significant as compared to all the other environmental variables. Similarly, a Delphi analysis in Iowa found out that a “mountainous topography” was the most significant factor during consideration for shorter paths and suitable routes (Souleyrette, Anderson, Hans, Mescher, Roeth & Thompson 1996). A hilly or a rolling topography, on the other hand, was found to be a factor of less significance to be considered by cyclists. According to Menghini et al. (2009), topography, street gradient, was a factor that was greatly considered by cyclists when choosing their routes. A combination of GPS and GIS analysis was applied and compared with the actual routes of the cyclists. Similarly, Celvero & Duncan (2003) found out that the decision to use bike paths was mainly influenced by the slope.
Gray & Bunker (2005) conducted a study using GIS analysis to select the common routes used by commuters. In the study, the researchers collected data from a number of sources that included the public transport route, transport timetables, bikeway data and services, public domain aerial photographs and infrastructural benchmarks. Analysis of the data was able to reveal the most appropriate routes to Brisbane’s CBD, unsafe bicycle rules and locations for new routes. This study shows that a rider can determine which routes to use and which ones to avoid using GIS (Gray & Bunker, 2005). Yamashita et al. (1998) applied DEM (Digital Terrain Model) integrated in GIS to create slope values that form part of road segments. The subsequent information on slope category was subsequently added to each section of the street network across the study zone with the help of Modular GIS Environment (Grid Analysis MGE). Yamashita et al., (1998) further estimated the length attribute of the links to the roads built on a slope and planar distance by including a street network file. Further, the MGE Network Analysis module was used to find the routes that are most ideal between two points. This approach by the researchers was advantageous given that it led to the creation of a dataset of citywide street network with gradient data for each of the sections.
A number of factors are usually considered by cyclists when choosing routes to be used. Such factors include the slope, characteristics of the roads, environment, traffic and the route itself as shown in Table 1 below:
Source: Segadihla & Sanches (2014).
As it can be seen from the table 1 above, factors such as slope, road characteristics and pavements are very important to the bicyclists. Shankwiler (2006) established that many bicyclists preferred two-lane streets to wider roads. When it comes to the gradient of the road or the slope, it was established that the presence of an uphill stretch affects the route choice as the steep hills increases the effort of pedaling. It is for this reason that many cyclists avoid routes and paths with steep slopes (Menghini Carrasco, Schüssler, & Axhau, 2010). In their research, Stinson & Bhat found out those non-experienced cyclists preferred flat roads. On the other hand, the more experienced cyclists preferred steep slopes as they provided physical exercise. In a study by Broach et al., (2012) in Portland, Oregon, the researchers found out that the slope of the road was the most considered factor in choosing a road by a cyclist. Further, the researchers acknowledged that some of the more experienced cyclists were willing to ride 37% longer distances on flat routes so as to avoid slopes that are greater than 2% (Broach et al., 2012). Nonetheless, Winters, Brauer, Setton, and Teschke (2010) revealed that there was a lack of consensus with respect to gradient that is considered not suitable for bicyclists. A cyclist always aims for minimal travel distance. Also, a cyclist prefers minimal trip time as it implies the usage of little energy and effort (Haustein, 2013). An average cyclist would prefer safety over distance any time. Grade has been found to be another important factor of consideration by cyclists when choosing routes. For example, a steeper grade implies that a road is rarely used by cyclists.
Travel Time
Haustein (2013) established that minimal trip time is important to cyclists as it implies less effort and energy being used. Ellison & Greaves (2011) found out that the travel time factor influenced the cyclists’ decision for route choice and travel. Travel time has been found to greatly influence the competitiveness of bicycles and this competitiveness can be calculated using both empirical and hypothetical approaches. Sener, Eluru & Bhat (2009) further argued that travel time is very important to cyclists given that it is relative to the amount of distance travelled and the amount of energy used. On a similar note, Winters (2011) found out that a majority of the cyclists considered 30 minutes to be the optimum time for a cycling trip. A survey conducted in Texas by Sener (2009) established that the younger population (18-34) found travel time more effective as they preferred shorter distances of travel in terms of duration as compared to the adult population. Power must be considered when estimating the time and costs.
A study by Levisnson & Wu (2003) based on the Rational Locator Hypothesis which states that people are more likely to uphold a steady journey-to-work travel times as soon as they adjust their home and work distance, found that people were willing to cycle in as long as the distance was short and the travel cost was small. For instance, when the distance between Twin Cities was reduced, the amount of time spent when travelling reduced immensely. In a controlled geographical location, it was found out that the travel time increased from eight four minutes to ninety minutes. The conclusion made from the findings was that the time of travel remains the same when an individual rides a bicycle from one point to another in a flat road.
Travel Cost
Literature on transportation economics and behavior of travel has established that bicyclists often make decisions about when, where and how to travel based on the concepts of generalized costs of travel and travel impedance ((Hanson 2004; Iseki & Tingstrom, 2012; Iseki & Taylor 2009). Further, a research study by Iseki and Tingstrom (2012) found out that travel impedance together with the generalized costs of travel reveal a number of issues that bicyclists often face such as the physical costs and the energy used in travelling. It is a common assumption that bicyclists are required to use the shortest routes possible in order to reduce the time of travel and the travel distance. Nevertheless, when considering travel time and travel cost, it is always important to factor in altitude change so as to effectively measure the distance between two locations in a flat surface. Further, Iseki & Tingstrom (2012) noted that most of the time data on travel time is usually not available and hence it is highly important to identify the factor that causes travel impedance in order to effectively and accurately estimate the generalized cost of travel by a cyclist.
Travel time budget is another issue that is important in travel cost. Ellison and Greaves (2011) defined travel time budget as the total amount of time that an individual is willing or is able to travel on a single day. However, it should be noted that travel time budget varies from person to person and the location. Ellison & Greaves noted that travel time is estimated to be around one hour per day. On average, travel time budgets are estimated to 80 minutes a single day although this may vary depending on travelled distance and the terrain. Also, travel budgets vary due to the age and characteristics of a person but have been found stable by the density of the population (Levinson & Wu, 2005).
Speed
Slope has a significant effect on speed; when cycling downwards in a steep slope, the speed increases but decreases when cycling upwards. Additionally, more energy is needed when going up a slope as compared to when going down (Ellison & Greaves, 2011). Additionally, steep and long gradients are difficult to cycle up hence reducing speed. For example, travelling at a flat distance, the speed is usually 16km/h but this gradually increases, 16km/h + 5(1.44). but declies up the slope 16km/h – 5(1.44) as shown in Fig 1 below.
Figure 1: Effects of gradient on speed
Source: Ellison and Greaves (2011).
Length (Easiest Path Analysis)
The easiest path is one that is shortest and requires the least amount of travel time. Martello (2009) found out that travel cost, travel time and travel distance are the traditional impedances often applied in network analysis. These factors have an effect on the travelling degree. In Martello’s study, several origin and destinations were analyzed and the easiest path analysis conducted. The analysis is applied to determine the shortest path that is less sensitive to steep grades and minimizes time in selecting a path or route. The cost of impedance is considered during the calculation of the easiest path analysis. Huang & Ye (1995) argued that since impedance is not desirable, it is necessary for the path with the least impedance from origin to destination to be a representative of the most desirable route by cyclists from origin to destination.
Methods for slope based bike path segmentation
The current bicycle models hold the assumption that the average speed along and among routes, and travel time is proportional to distance (Tokmylenko, 2013). Nevertheless, no method out there realistically determines the cycling time based on the speed change because of topography. A number of researchers have investigated the influence of topography on bicycle cycling and majorities are in conclusion that topography causes travel impediments, especially the steep slopes.
In their study, Huang & Ye (1995) established that bicyclists were more sensitive to slope as compared to motorists. The further noted that the conventional methods of calculating slope Arc/info fail to take into account the direction of the streets as they only give the surface slope. Consequently, in making calculations, each street’s slope must be taken into consideration in collection of the necessary data. Huang & Ye applied the formula:
Where Sab is the slope between the original point a and the final point b; ha represents the elevation at point a; hb the elevation at point b and lab is the distance between the two points a and b.
Methods for Assessing Path Segment’s Level of Difficulty
Types of Cyclists
Bicyclists have been evaluated by the American Association of State Highway and Transportation Officials (AASHTO) according to their age, skills and comfort levels (AASHTO, 2012). However, these characteristics fail to take into account the physical abilities of the bicyclists. Advanced cyclists are people who have used the same routes for motorized traffic for a long time. Nonetheless, this criterion cannot be used to categorize cyclists that use steep slopes (AASHTO, 2012). The purpose of the trip also has an effect on cyclists’ behaviour. Tokmylenko (2013) takes note of the fact that AASHTO and FHWA (Federal Highway Administration) have differentiated the recreational and utilitarian purposes. Cyclists that use bicycles as a means of transport are categorized as using them for utilitarian purposes. Travel time and distance covered are factors used in analysing these cyclists. The recreational purposes of cycling are for exposure and pleasure. Utilitarian cyclists value the efficiency and effectiveness of the trip while recreational riders value the safety and quality of the ride.
The FHWA classifies cyclists based on a number of factors that include the slope, the level of comfort, usage and the levels of stress of the bicycle (Harkey, Reinfurt, Knuiman, Stewart, & Sorton, 1998). The FHWA hence classifies cyclists into Group A, Group B and Group C. The “Group A” cyclists are those considered to be confident and advanced. This group comprises of adult cyclists that are confident in riding and they can use their cycling in different environments. These cyclists can ride in motorized routes comfortably. They require minimum safety levels and care less about the quality of the routes. Group B cyclists comprises of cyclists with basic and limited skills. They include the youth and teenagers who are less confident in their riding skills. These cyclists care about the quality of the facilities, have higher safety levels and would prefer to cycle in a separate path or route. The last group, C, comprises of children who are usually escorted by their parents. They are the most vulnerable of all the cyclists.
A number of authors have come up with other classes. For instance, a study in Vancouver categorized riders based on the frequency of their riding. Riders were categorized as regular, occasional, frequent and potential riders. Regular are the ones that cycle at least once a week; ≥ 52 trips per year. Frequent cyclists are those that cycle once a month, 12-51 trips a single year. Occasional cyclists are those that ride a bicycle at least once a year; 1-11 trips on a sinle year. Potential riders are those that have not rode a bicycle in a year, have the access to a bicycle and contemplate using the bicycle in the near future. Tolley (2003) and Tokmylenko (2013) established that the regular cyclists are well developed physically as consistent cycling has numerous benefits health-wise. Other ways of evaluating cyclists also exists. For example, Tokmylenko (2013) found out that sports-based websites such as, www.cyclingpowerlab.com, categorized cyclists based on their proficiency levels and the years they have been active. Cyclists, for example, fall into the categories beginners, non-racing cyclists and elite racing cyclists.
Criteria of Slope Gradient
Gradient, in cycling, refers to the steepness of a road section. A flat road has a zero per cent gradient while a road with a higher gradient for example 10% is steeper than one with a 4% gradient. Gradient greatly affects cycling and may cause travel impedance (Smith Jr, 1975). A steeper road requires more energy and effort to ride. A slope also affects the speed of a bicycle as going down a road with a steep slope means a higher speed that may cause safety problems for an inexperienced rider. Riders are very sensitive to slope and hence they choose routes and paths that they are most comfortable riding in (Smith Jr, 1975). Roads with a gradient of over 5% difficult for riders while those with a 2% gradient are suitable for many riders (Litman et al., 2016). Riders have to contend with a number of guidelines that have been put forth to enable them ride easily and safely.
The International Mountain Bicycling Association (IMBA) has developed a trail difficulty rating system to guide planners in developing routes and cyclists in choosing routes to use. IMBA factored in the trail grade as an important aspect in assessing difficulty and found that the average grade for all cyclists to be 3%. A 3% grade can be used by both beginners, skilled, experienced and highly experienced cyclists (IMBA, 2012). Gicycle (2016) takes note of the fact that topography greatly affects the choice of routes and paths, and the fact that slopes affect speed and safety. In so doing they developed a model of assessing slopes and categorized slopes into the following categories: level, little slope, gentle slope, steep slope and very steep slope. A level slope and little slope are suitable for all cyclists since it is easy to ride. A gentle slope is suitable for riders with intermediate skills since it is more difficult. A steep slope is associated with riders with advanced skills due to its high level of difficulty. A very steep slope is suitable for riders with exceptional riding skills. Using this scale, bicyclists are able to choose the most appropriate route to use. The scale is shown in the figure below:
Source: Gicycle (2016).
The Austroads Guide to Road Design on bicycle paths emphasizes that steep slopes are a potential hazard and barrier to riders and should be avoided. The guide states that gradients that are steeper than 5% should be avoided unless it is a must to use them. The guide also takes note of the fact that an uphill rise for cyclists starts to become difficult at grades above 3% and become impossible at 5% grades and above. It goes ahead to state that grades of 3% are the maximum desirable grades for a cyclists path (Bicycle Network, 2016).
GIS-Based Approaches
Gradient and aspect are the primary components of a slope. According to Hickey (2000), gradient is the maximum rate of change that is realized on the elevation of a plane while aspect is the place direction with reference to arbitrary zero. In undertaking environmental analyses, calculations of the length of the slope and the angle are very important. GIS technology has widely been applied to calculate angle and length due to its versatility and its power to process spatial data (Qiu, Esaki, Xie, Mitani & Wang 2006). GIS also provides a strong function for the processing of data and geo-statistical analysis. The challenges encountered in applying deterministic models have encouraged the use of GIS technologies to obtain process and check large spatial data sets, and resolve any problems related to geospatial data. GIS is used in slope analysis and can be applied using a number of variables to determine bicycling in cities and towns. Moudon et al., (2005) sought to determine the relationship between cycling and the environment and considered variables such as distance to the neighborhood centers, land use, safety and how frequent people use buses. Other variables that were considered included the length of the sidewalk, traffic volume and speed, population density, topography and size of the street block. GIS was able to provide information on the frequency of bicycle rides in a week or month. GIS has and is producing information used in planning of the city.
Through GIS technologies we are able to select bicycle paths and routes. It also provides a wonderful opportunity to computerize the process of lane selection and routes. Huang & Ye (1995) embarked on a study to develop a method that could be used to select the most appropriate paths for bicyclists. The study revealed that GIS is an important tool in developing a data base that could be used effectively in route and path selection (Huang & Ye, 1995). Cyclists are more sensitive to surface quality and the slope. Application of GIS technologies in bicycle route planning requires more data layers as compared to vehicle routes, hence making it a different form of planning. After data collection using GIS, it was possible incorporate other valuable information from institutions and government agencies. GIS is now widely used to perform spatial operations such as terrain modeling and analysis of networks.
Conclusions
The existing literature shows that the current methods being used to plan for bicycle infrastructure do not take into account the factors affecting cycling. Many planners often take into account economic feasibility and safety only, but a number of factors are being left out. As research reveals, factors such as the gradient slope, travel time and cost, length of routes and speed greatly affect bike riding. For instance, a steeper slope increases travel impedance as more energy and effort will be needed to go through it. GIS technologies have proven essential in bike riding as they are able to map out the locations hence enabling riders to move from place to place with ease. Additionally, with GPS and GIS, it has been possible to establish the easiest and shortest route for cyclists from one location to another. Besides, GIS analytics have also ensured that hazards along paths and routes are mapped out and hence enabling bicycle riders to avoid accidents.
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