Q. Can you tell me how long the walk light should stay on for pedestrians to walk across a highway once the button is pushed to allow for crossing? The South County bike path ending at Route 108 has a button near the sidewalk for folks to push to get a walk signal but once the light goes on it does not allow ample time for a pedestrian to walk across before cars come at them from Route 108. Sometimes the walk signal lights up and the green signal is lit for cars to process out of McArthur Boulevard. As a 78-year-old who has several times had to run across, what can you do?

A. RIDOT visited this site and added some time to the pedestrian walk phase of the pedestrian signal.

The white walk symbol, typically the image of a person walking, will be steady for a few seconds. This indicates to the pedestrian that they should start to cross the road.

The orange don’t walk symbol, typically the image of a hand, will flash. The time that the hand flashes accounts for the time a pedestrian takes to cross the street from one curb to the other curb. If a pedestrian starts walking when the walk signal first appears they should have enough time to safely finish crossing the street. Pedestrians should not start crossing the street once the signal begins to flash as they may not have enough time to complete the crossing.

Once the bike path is open on the east side of Kingstown Road in fall 2010, the Department will make any additional changes that are deemed necessary.

Signals explained

Q. Is there a standard on how a long it takes to switch from a yellow traffic signal to a red traffic signal and how long that red light stays on? Are traffic signals certified annually? Also, I noticed many new lights are fixed at opposite corners versus the middle of the intersection. Is time allowed for this distance?

A. Yes, there are standards for how long a traffic signal remains yellow and red. The length of each of the lights is based mostly on the average vehicle speed and the width of the intersection. The lights are shortest on slow narrow roads and longest on faster wider roads to reduce the potential for dangerous accidents.

Traffic signals are not certified regularly, but they are monitored frequently to make sure that the equipment is working properly and that traffic is moving without much difficulty.

As far as the location of traffic signals in the intersection, whether the signal is hung over the intersection or mounted in the opposite corner of the intersection will not affect the length of the yellow or red light. The lights mounted at the opposite corner of the intersection are not significantly further from the driver compared to the lights hung over the intersection, so the lights are not timed differently.

The most important factor in timing yellow and red lights is that drivers have enough time to reduce their speed to stop or have enough time to safely clear the intersection.

Dana Alexander Nolfe, chief public affairs officer for the state Department of Transportation, has agreed to answer questions of general interest posed by Journal readers about state roads and other state transportation matters.

The DOT is responsible for the state’s transportation infrastructure, which includes highways, bridges, traffic signals and bikeways.

Questions are answered in the order they are received, and there may be a delay in answering.

To ask a question that would also be of interest to other readers, send a letter to Ask RIDOT, Features Department, The Providence Journal, 75 Fountain St., Providence, RI 02902. You can also e-mail your question to projocars@projo.com. Please put “Question for the DOT” in the subject field.

Questions or complaints of a specific nature should be posed to the DOT directly and will not be answered in this column.