Width of cycle paths: Analysis of behavior and capacity
by Thomas Skallebæk Buch and Poul Greibe
Summary and conclusion
This report presents a study of cycle paths with regard to the relationship between path widths and behavior and capacity. The study is financed by the Bicycle Pool.
The background to the project is that bicycle traffic is growing and the number of specialized bicycles is increasing. At the same time, there is a societal interest in promoting bicycle traffic. In Denmark, the recommended values for cycle path capacity are based on older studies from the 1940s, and both Danish and international studies give very different estimates of cycle path widths, average speeds and capacity. Part of the explanation is differences in cycling behavior and bicycle design between countries, but methodological choices also play a role.
The main purpose of the project is therefore to contribute new knowledge about the effect of bicycle path width on driving behavior, accessibility and capacity. The aim is to translate this knowledge into indicative dimensions for cycle paths depending on the size and composition of bicycle traffic and the desired accessibility for cyclists.
In this project, empirical data from 8 one-way bicycle paths along roads in urban areas were used. Data is collected by video registration in two measurement sections (approx. 20 meters apart), where the speed of the path users is measured between the two measurement sections, and the lateral position of the path users is measured in one measurement section.
The 8 sites were selected on the basis of several criteria, the most important of which are: large volumes of bicycle traffic, curb separation to both road and sidewalk and uninterrupted paths both before and after the registration site. In order to maximize traffic volumes, path traffic was recorded during rush hour, and the sites were all located in central Copenhagen and Frederiksberg. The locations differ by having different path widths (1.85-2.85 meters (excl. curb)) and the use of the road area on the other side of the curb is different (roadway or parking).
Data were collected in summer 2013. A total of 8,925 path users were registered, 900-1,300 per location. The cyclists are distributed by type: ordinary bicycles (virtually all types of 2-wheeled bicycles), special bicycles (3-wheeled cargo bikes and bicycles with 2-wheel trailers), mopeds and others.
Footpath users are considered to be free-moving if the time distance to the nearest preceding as well as following footpath user is at least 2 seconds. If the pedestrian is driving next to another road user and has an overlap when crossing the measurement section (overtaking or following), this is recorded and the position of the pedestrian is numbered with the lowest number for the road user closest to the pavement. Only in a few cases and only on the four widest paths, a pedestrian is recorded in position 3.
The vast majority (about 98 %) of the survey's path users are ordinary bicycles, while special bicycles account for 1.5 %. Similarly, about 98% of cyclists are adults, while children as well as elderly people each account for about 1%. There is a slight predominance of women.
The study shows that the proportion of the path area used by cyclists is reduced if cars are parked along the cycle path instead of the carriageway. The impact can vary depending on how close a car is parked to the cycle path, but the effective path width is reduced by 10-15 centimetres in the case of parked vehicles along the cycle path. Therefore, where results are compared with path width, the effective path width is used, where the width is reduced by 12 centimeters in the case of parked vehicles along the path.
For regular bicycles, there is a linear relationship between distance to pavement and path width when positioned in position 1 and position 2. If the path width is increased by 10 centimeters, the cyclist in position 1 is 1.8 centimeters further from the pavement, while the lateral distance between overlapping cyclists is increased by 2.7 centimeters. The dispersion also increases as the path width increases.
Free-riding cyclists generally keep right on the path, but they keep a greater distance to the sidewalk than cyclists in position 1. There seems to be a tendency for greater distances to the pavement on the widest paths, but there is no linear relationship.
The utilization of the path width increases with increasing traffic volumes. At low traffic volumes, up to 90% of cyclists are in lane 1, while at the highest traffic volumes (more than 12 bicycles per 10 seconds), only slightly more than half of them are in lane 1. The lanes are narrower and more well-defined on the narrowest paths in the study, where there are only 2 lanes. The three sites with path widths of around 2.5 meters function primarily as 2-track even under high traffic intensity, while the widest path (2.85 meters) is not observed at sufficiently high traffic volumes to assess whether it has 2 or 3 tracks.
The average speed of ordinary bicycles in the survey is 21.7 km/h (20.2-23.7 km/h depending on location). The vast majority of cyclists travel between 17 and 27 km/h. There is a tendency for cyclists to position themselves closer to the pavement the slower they ride, which is also observed for free riders. In addition, there seems to be a tendency for higher speeds with increased path widths, but the correlation is not clear.
Ordinary bicycles in position 1 travel 3.2-4.8 km/h slower than bicycles in position 2. Freewheelers travel on average at a speed between these, and the spread is wider. Women generally ride slower than men. Among free riders, the difference is 2.7-4.5 km/h depending on the route, and for all routes the smallest spread is seen among women. This could indicate that there is a predominance of men among fast cyclists. For each section, a more uniform speed level is seen at higher traffic intensities, but no traffic volumes are observed that are so high that an actual breakdown with low speed occurs as a result. The passability seems to be 5-10% higher on a 2-lane path with a width of 2.75 meters compared to a path with a width of 1.75 meters.
The maximum observed flow (max-flow) seems to increase with increasing effective path width, but the path width seems to have little effect. The capacity of a 2.0 meter wide path (excluding curb) is about 3,000 bicycles per hour, which is more than the 2,000 bicycles per hour in the road rules, but significantly less than the estimates in other studies (typically 4-7,000 bicycles per hour). A 2.5 meter wide path is estimated to have a slightly higher capacity of 3,250 bicycles per hour. For a 2-lane path, it is assumed that each lane can handle approximately 1,500 bicycles per hour. Thus, a 3-lane path will probably be able to handle approx. 4,500 bicycles per hour.
As with regular bicycles, special bicycles tend to keep more to the right when they are in position 1 of the overlap than when they are freewheeling. There is a tendency for special bikes to choose a greater distance to the sidewalk as the path width increases. The special bikes occupy about 10-20 centimeters more of the path width than regular bikes. On average, special bikes travel at significantly lower speeds than regular bikes, 16.3 km/h compared to 21.7 km/h. The presence of special bikes seems to affect the flow in lane 2, as regular bikes in position 2 seem to have a lower speed when overlapping with a special bike in position 1 rather than a regular bike. Special bikes reduce the speed of regular bikes on the narrow paths at both high and low traffic intensity. A special bike seems to reduce maxflow by 3-4 regular bikes, but its headway in lane 1 is 1.2 times that of a regular bike.
Cycle path widths
Based on the survey data, the following suggestions for target path widths for a 2-lane cycle path are given:
- Minimum (no/few special bikes): 1.65 meters (excluding curbs)
- Minimum (space for special bikes): 1.80 meters (excluding curb)
- Recommended width (higher level of service): 2.10 meters (excluding curbs)
The widths are broadly in line with the road code recommendations of minimum 1.70 meters (only for shorter sections) and recommended 2.20 meters. Cars parked along the path result in a necessary allowance of 10-15 centimeters.
The minimum width for a 3-lane cycle path is expected to be 2.90 meters (excluding curb). On a slightly narrower path, three bicycles can ride next to each other, but it is not expected that the path will function as a true 3-lane path. The allowance for an additional lane on the cycle path is expected to be about 1.10 meters. This is at the higher end compared to other studies.