How long does it take to cross the street?
It is surprisingly difficult to determine how long it takes a pedestrian to safely cross the street at a zebra crossing.
Traffic engineers calculate this time using a number of formulas that take into account the width of the street, average walking pace, and intersection design, among other things.
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These calculations had previously assumed that walkers and rollers could travel 3.5 feet per second from the top of a curb ramp to the other side before the light changed.
In talking to a pedestrian advisory group, the Seattle Department of Transportation updated its guidelines to give people a little more time to cross – a move that is celebrated by advocates for the elderly and the disabled.
The change is an example of what appears to be a small change that pedestrian advocates claim can make a big difference in road safety without the need for major construction or cost.
“It’s a really good step in the right direction,” said Anna Zivarts, director of the Disability Mobility Initiative at Disability Rights Washington, which was part of the group advising SDOT. “I think it will make crossing the street a lot safer and more comfortable for a lot of people.”
Lars Sveum-Hanson, 74, welcomes the change. He lives in the senior residences at Cedar Park in Lake City and said the walking conditions in the neighborhood put me in some unsafe situations.
Before going to the bank or Lake City Presbyterian Church for music and film lessons, Sveum-Hanson wore a rainbow-colored hat and bright orange vest that he had kept from his time as a bus driver in Minnesota.
But even with vibrant clothing and accessories, he still fears getting hit while crossing the street.
“I’m pretty agile and still the meter almost always runs out before I get to the other side,” he said.
Akira Ohiso, a social worker at Sound Generations, an organization that offers activities for the elderly, said he regularly sees elderly people struggling to cross streets before the lights change.
“Crosswalks in busy urban streets do not allow older adults enough time to cross safely, especially four-lane roads,” he said.
According to the new guidelines from SDOT, signals with the updated formulas will be rescheduled when existing intersections are changed, when community members request a change and when new signals are installed.
The city uses two different formulas to determine how long pedestrians can cross the street, and it can get a little tricky.
To see how this works, consider the new signposted intersection at Northeast 125th Street and 28th Avenue Northeast in Lake City.
In Northeast 125th Street, the new guidelines require hikers to cross a total of 22 seconds – eight seconds for the steady “Walk” signal and 14 seconds for the flashing “Don’t Walk” signal.
The minimum time for the “walk” signal is seven seconds. However, SDOT can add more time depending on road width and other conditions. At the 125th northeast, the time is eight seconds, said Dusty Rasmussen, a traffic signal engineer at SDOT.
The time for the blinking “Don’t Walk” signal is based on the width of the road and the new assumption that most hikers can travel 3 feet per second – a slightly slower speed than the old guidelines.
The distance between the tops of the curb ramps on either side of the northeast 125 is 42 feet. So if you divide 42 by 3, you will get a 14 second flashing “don’t go”. The idea is to give pedestrians time to clear the intersection if they enter the zebra crossing when the flashing signal starts.
The engineers then use a different set of calculations to check whether the total traverse time – that is, the “Go” signal plus the blinking “Don’t go” signal or the red blinking hand – is sufficient.
First, they measure the distance from the push-to-walk button on one side of the street to the top of the curb ramp on the other side. That’s 48 feet to the northeast 125. You use this measurement because a visually or hearing impaired person may need to stand farther from the curb to feel the vibrations of the push button, which signals when it is safe to walk.
The engineers take that distance and divide it by 2.5 – assuming that most people can walk or roll 2.5 feet per second. For the 125th northeast, 48 feet divided by 2.5 seconds per foot equals 19.2 seconds of total walking time.
This confirms the 22 second override time is within guidelines, Rasmussen said. If the calculation resulted in a number less than 19.2 seconds, the engineers would add more time to the run signal.
After 22 seconds, the flashing signal will turn into a steady “don’t go” signal. Cross traffic receives the green light a few seconds later.
The changes to SDOT’s zebra crossing will mostly offset each other for drivers, meaning slightly longer red lights will usually result in longer green lights, said spokesman Ethan Bergerson.
Zivarts said the lightbulbs like the ones along Dexter Avenue and Nickerson Street not only increase crossing time, but also shorten the length of the zebra crossing and make it easier to cross.
The longer crossing times build on an earlier initiative that gave pedestrians a few seconds head start on the intersection before cars and trucks traveling on the same route are given the green light. The protrusion is intended to make pedestrians more visible on the zebra crossing.
The latest changes also shed more light on whether pedestrian signals should be automatic as part of the traffic cycle or based on push-to-walk buttons.
An automatic foot signal will be used in busy parts of the city and in some cases during busy times of the day according to the new policy.
A push-to-walk button may be more suitable in an area with fewer pedestrians.