Daylight Savings ends on Sunday, and with it the light in the evening. Daylight savings, as many of you know, exists as part of an energy savings program and was last expanded as part of the 2005 Energy Bill. There is some debate as to whether it has led to less electricity use or not. A 2008 study by the Department of Energy said it decreased energy use by 0.03%, but others say it increases energy use by 1% or more. [I don't understand how, in the name of good energy policy, we can literally change time, but we can't get a carbon tax, but that's another issue].
So what does this change do to bike commuting. Next week, most bike commuters will ride home in the dark. And many will bike to work in the dark too. Winter is a more dangerous time to bike commute for this reason. Does daylight savings make it more dangerous? Does it dissuade bike commuters?
One study - based on data from Arlington's bike counters (hooray local government) - showed that changes in light resulted in changes in bike and walk commuting. And that the number of people actively commuting changed significantly near the clock change, with people doing less of it when it is dark. This change was lower for cyclists than pedestrians.
Odds ratios indicated the numbers of pedestrians and cyclists during the case period were significantly higher during daylight conditions than after-dark, resulting in a 62% increase in pedestrians and a 38% increase in cyclists.
There are large peaks in cyclist frequencies at morning and evening commuter times, and whether the case hour is in daylight or darkness does not alter the timing of these peaks. This supports the suggestion that cyclists may be quite rigid in their travel times, producing a relatively limited spillover effect.
They also believe that lighting plays a part in this because trail commuting goes down more than on-road commuting.
the transition between darkness and daylight during the case period had a greater effect on cyclist frequencies at trail locations, compared with cycle lane locations.
Meaning that one conclusion is that we need more lighting on bike commuter routes (recognizing that it should be environmentally appropriate) if we want more people to bike commute in the winter.
Another conclusion the studies show is that it is darkness, more than the cold, that causes bike commuting to drop in the winter (which echoes my opinion that it's the dark that I find more unpleasant than the temperature). When non-cyclists argue that people won't bike all year, they talk about the cold, but this indicates that they're wrong, and may explain why biking commuting doesn't 1) go down when it gets really hot 2) go down more in colder climate cities than warmer ones.
The transition in ambient light condition alone can explain the increase in pedestrians and cyclists during the daylight periods independently from any influence of temperature. In fact, the clock changes that showed no change in temperature generally produced larger odds ratios than those clock changes where the temperature did change significantly. This would suggest the effect of the transition in light conditions was larger when there was no temperature change.
This means that the more that we can move the rush hours into daylight, the more we'll encourage active transportation. Next week, we'll lose light in the evening rush in exchange for an hour in the morning rush, but I feel like it's not a good trade. We give up 5-6pm for 6:30-7:30am and you can see from that bicycle counter data that this is a bad trade. We give up our 2nd (and nearly top) biking hour in the evening in exchange for a mid-level hour in the morning. We're also giving up a time that many kids are being picked up from daycare and aftercare and also more likely to be out and about, for a time when many are still asleep or at home. Like I said, I think it's a bad trade.
So daylight savings has some impact on how many people commute, but what about safety? Unsurprisingly, this has been studied in the US and unsurprisingly, having light at the time when more people commute is expected to save lives.
Results show that full year daylight saving time would reduce pedestrian fatalities by 171 per year, or by 13% of all pedestrian fatalities in the 5:00–10.00 a.m. and in the 4:00–9:00 p.m. time periods. Motor vehicle occupant fatalities would be reduced by 195 per year, or 3%, during the same time periods.
Same in the UK
operating daylight saving year-round would have a small but tangible effect on the number of serious and fatal road traffic injuries in children in this area.
And of just pedestrians
there was a significantly greater risk of a pedestrian [road traffic collisions] at a crossing after-dark than during daylight.
Other studies indicate that this isn't due to changes in Circadian rhythm. The shift in sleep leads to an increase in accidents in the spring and a decrease in the fall.
The spring shift to daylight savings time, and the concomitant loss of one hour of sleep, resulted in an average increase in traffic accidents of approximately 8 percent, whereas the fall shift resulted in a decrease in accidents of approximately the same magnitude immediately after the time shift.
Though it's not a local issue, we should consider extending daylight savings year round. There's a question about what that does to energy consumption and that might require a trade off; but it does seem it would make the roads safer and encourage more bike commuting and walk commuting (which could offset any energy impacts).
Even if we don't change daylight savings, we need to install brighter and better lighting on bike routes, pedestrian commuter routes and at crosswalks.
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