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Cyclists on bus lanes: a safe idea?

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Sharing is (s)caring. Since 2002, cyclists are allowed on bus lanes. This policy measure was a compromise between the needs of road users and the available space. Urban areas often don’t dispose of enough space to construct a lane for each individual road user. Although the policy measure practically solved the lack of space, the different speed profile of cyclists and buses worries the government. Cyclists retain a slow, constant speed, while buses alternately accelerate and stop. IMOB studied the impact of shared bus lanes on road safety of cyclists. Does it cause unsafe situations? Is there a difference between narrow and wide bus lanes?

According to Flemish guidelines: a bus lane should be smaller than 3,5m or wider than 4,5m
IMOB drew inspiration from foreign and domestic guidelines to define small and wide bus lanes. Flanders prescribes that a bus lane should be smaller than 3,5m and wider than 4,5m to guarantee the road safety of cyclists. At bus lanes smaller than 3,5 m, a bus driver can only overtake when leaving the lanes. The Flemish government disapproves bus lanes with a width between 3,5m and 4,5m. They are too narrow to overtake cyclists within the bus lane and to respect a safe overtaking distance at the same time. The minimum width abroad depends on other factors such as speed limit and lays between 3,7m and 5m.

Three factors point at an (un)safe situation
The overtaking distance between bike and bus, the speed of the bus while overtaking and the time of headway (when driving behind the cyclist) are factors that reveal something about the road safety. The researchers categorised a time of headway less than 2s as dangerous. IMOB applied those factors on two, Flemish bus lanes. One is located in Kortrijk and is in accordance with the Flemish guidelines (width: 3,10m). The other bus lane is located in Ghent and doesn’t meet the guidelines (width: 4,20m). IMOB investigated the impact of the presence of a bus on road safety of cyclists and compared those situations to situations where cyclists weren’t followed or overtaken. The results are clear. Bus lanes with shared use by cyclists may be a practical solution, it has a possible negative influence on road safety of cyclists.

Cyclists adapt their driving behaviour
The results have shown that cyclists adapt their driving behaviour in the presence of an approaching bus. They drove closer to the edge of the lane and adjusted their speed. How and when they adjusted their speed, depends on the situation. On a narrow bus lane, they cycled more quickly when being followed by a bus. On a wider bus lane, they cycled more quickly when being overtaken. Furthermore, dangerous times of headway were recorded. More than half the situations where a bus followed a cyclist, had a time of headway less than 2s. Almost a quarter of the bus drivers followed a cyclist on less than 1s.

Safety narrow bus lanes not confirmed
The guidelines underlined the importance of narrow bus lanes (<3,5m). However, in this study, the safety of narrow bus lanes was not confirmed. It even seems that unsafe situations (overtaking and following) occurred more often on narrow bus lanes. A average bus driver retains a safe overtaking distance of 1m. The overtaking distances varied more at narrow bus lanes and this design evokes more follow situations, but buses on wide bus lanes overtook cyclists at a higher speed. Therefore, IMOB cannot indicate unequivocally which design is – from a safety viewpoint – to be recommended.

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