Buses and speed-limiting
Sep. 3rd, 2017 04:19 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
julietThe other day someone linked me to this report on a trial of Intelligent Speed Assistance on London buses. ISA uses GPS to obtain data on where you are and thus what speed limits apply, and then compares that with the speedometer, and either makes a nuisance of itself warning the driver that they're speeding, or (as in this case) actively limits the speed to the speed limit.
The first thing that stood out to me from the summary was that "the percentage of time buses spent travelling above the speed limit reduced from a range of 14.9-17.8% to 1-3.3% in 20mph zones, and 0.5-3.3% to 0-1.1% in 30mph zones". This matches my own anecdotal impression that 20mph limits (increasingly common in London) are moderately commonly exceeded even by professional drivers. There are detailed graphs on p20-1 of the report which clearly show buses happily going up to 30mph and even slightly above in 20mph zones.
Also, "the study found a marginal (1.4%) increase in route journey times for route 19, which could potentially require more buses on this route. ISA will highlight any existing issues with route timings. If TfL was to implement ISA London-wide for all bus routes there would be a requirement to calculate the impact of ISA separately for all routes". If buses are only making their current timetables by speeding (and ISA should only be slowing them down if this is the case) then YES, the bus timings will need to be changed. Driver comments later on suggest that drivers are routinely speeding to catch up with their timetables, which shouldn't be happening.
One of the summary comments on driver perception is: "Residual concerns remain relating to off-peak conditions when traffic is lighter and drivers' perception remain that other vehicles become frustrated at being held up by buses complying with the speed limit." The first half of that isn't clear to me, but it seems like drivers may feel that they shouldn't have to stick to the speed limit during off-peak times? And the second suggests to me that drivers at present are inclined to speed a bit because they think that other drivers find the speed limit too low. (Again I would be prepared to bet, given the figures, that this perception primarily applies to the 20mph limit.)
The quoted feedback from drivers later on in the report talks a lot about things like trying to overtake cyclists and not being able to (because they'd have to go over 20mph). They seem to see this as a major problem. Surely the answer is "don't overtake if you'll have to go over 20mph in a 20mph zone to do so"? The criticisms about the way the ISA operates (not just limiting but actively braking) are legitimate, but "I need to be able to break the speed limit sometimes" seems immensely dubious to me. Similarly, "other drivers don't like it": other drivers can sod off and stick to the speed limit themselves, no?
Because other drivers are, at present, failing to do so in significant numbers, e.g.: "the proportion of vehicles in the platoon [the vehicles immediately following the bus] exceeding the speed limit in 20mph zones falling from 51.1% to 42.0%" and "A vehicle gap did open up between the bus and the vehicle in front in the 20mph zones (not the 30mph zones), which suggests that the slower ISA-equipped buses could not keep up with vehicles in front". In short: many many people are speeding in 20mph zones. (A later comment suggests that speeds are "naturally higher" than the speed limit in mornings and evenings; rush hour I guess?) Unfortunately (p47) the overall average speed of other drivers doesn't change much, because there just aren't all that many buses.
More than anything else this strongly suggests to me that what TfL (& the police?) really need to be doing is enforcing 20mph zones, on everyone.
The first thing that stood out to me from the summary was that "the percentage of time buses spent travelling above the speed limit reduced from a range of 14.9-17.8% to 1-3.3% in 20mph zones, and 0.5-3.3% to 0-1.1% in 30mph zones". This matches my own anecdotal impression that 20mph limits (increasingly common in London) are moderately commonly exceeded even by professional drivers. There are detailed graphs on p20-1 of the report which clearly show buses happily going up to 30mph and even slightly above in 20mph zones.
Also, "the study found a marginal (1.4%) increase in route journey times for route 19, which could potentially require more buses on this route. ISA will highlight any existing issues with route timings. If TfL was to implement ISA London-wide for all bus routes there would be a requirement to calculate the impact of ISA separately for all routes". If buses are only making their current timetables by speeding (and ISA should only be slowing them down if this is the case) then YES, the bus timings will need to be changed. Driver comments later on suggest that drivers are routinely speeding to catch up with their timetables, which shouldn't be happening.
One of the summary comments on driver perception is: "Residual concerns remain relating to off-peak conditions when traffic is lighter and drivers' perception remain that other vehicles become frustrated at being held up by buses complying with the speed limit." The first half of that isn't clear to me, but it seems like drivers may feel that they shouldn't have to stick to the speed limit during off-peak times? And the second suggests to me that drivers at present are inclined to speed a bit because they think that other drivers find the speed limit too low. (Again I would be prepared to bet, given the figures, that this perception primarily applies to the 20mph limit.)
The quoted feedback from drivers later on in the report talks a lot about things like trying to overtake cyclists and not being able to (because they'd have to go over 20mph). They seem to see this as a major problem. Surely the answer is "don't overtake if you'll have to go over 20mph in a 20mph zone to do so"? The criticisms about the way the ISA operates (not just limiting but actively braking) are legitimate, but "I need to be able to break the speed limit sometimes" seems immensely dubious to me. Similarly, "other drivers don't like it": other drivers can sod off and stick to the speed limit themselves, no?
Because other drivers are, at present, failing to do so in significant numbers, e.g.: "the proportion of vehicles in the platoon [the vehicles immediately following the bus] exceeding the speed limit in 20mph zones falling from 51.1% to 42.0%" and "A vehicle gap did open up between the bus and the vehicle in front in the 20mph zones (not the 30mph zones), which suggests that the slower ISA-equipped buses could not keep up with vehicles in front". In short: many many people are speeding in 20mph zones. (A later comment suggests that speeds are "naturally higher" than the speed limit in mornings and evenings; rush hour I guess?) Unfortunately (p47) the overall average speed of other drivers doesn't change much, because there just aren't all that many buses.
More than anything else this strongly suggests to me that what TfL (& the police?) really need to be doing is enforcing 20mph zones, on everyone.
no subject
Date: 2017-09-03 04:51 pm (UTC)no subject
Date: 2017-09-03 07:15 pm (UTC)As a driver I would also quite like some heads-up display wherein my speed is projected into the windscreen glass. In the kind of street where a 20mph limit is certainly justified, I don't want to be taking my eyes off the road even for a moment to check my speed.
no subject
Date: 2017-09-11 06:01 am (UTC)no subject
Date: 2017-09-11 09:54 am (UTC)30/20/30 etc on the same road looks a bit like bad road design -- certainly doesn't encourage staying below the speed limit. Mind you there is some shocking road design in London (obviously especially in re bikes...) so I shouldn't be surprised.
no subject
Date: 2017-09-11 09:58 am (UTC)I feel obliged to say I only do this in my car when I'm providing assistance to a mobility impaired friend!!! Usually I'd be on the bike and in the bus lane.
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Date: 2017-09-04 06:04 pm (UTC)no subject
Date: 2017-09-05 04:21 am (UTC)no subject
Date: 2017-09-11 09:55 am (UTC)no subject
Date: 2017-09-11 10:04 am (UTC)no subject
Date: 2017-09-18 06:30 pm (UTC)no subject
Date: 2017-09-06 12:28 pm (UTC)