— Alan Bryski, Upper Macungie Township
First, a quick detour on a related road: Questions regarding traffic-signal timing or function have streamed into the Warrior's email garage more steadily than those representing any other category over the years, with suggestions for timing tweaks in particular creating traffic jams.
Calls for left-turn green arrows where they do not appear, and complaints about green phases that are too short to handle the traffic volume at particular intersections, lead the pack. Two basic answers apply to many of them.
Green arrows are installed only if specified warrants including traffic-volume and conflicting-traffic minimums are met, and the cost of adding the feature falls to the municipality where the signal is located. Green-arrow or other signal-change requests should be made to the relevant municipality.
The most common model of all goes something like, "the green light for traffic in my lane needs more time." PennDOT traffic-signals guru Tom Walter's familiar answer applies to most of those cases: For each second added in the direction you're traveling, a matching second must be subtracted from the green time afforded to opposing traffic. As Walter said many years ago, even the savviest traffic engineers can't create time: "There's only 60 seconds in a minute, and there's only so many ways we can divide them up."
That's not to say all signals are operating at peak efficiency. Traffic patterns change, sometimes phasing changes are needed, and sometimes officials even make those changes. But often, green phases seem too short at intersections that are so overburdened by traffic, particularly at peak times, that volume exceeds the capability of even the best-designed signals.
Your question is relevant now though, Alan, because the state Legislature is considering whether to allow the use of red-light cameras in cities other than Philadelphia — including Allentown, Bethlehem and Easton.
Yellow-signal phasing can be a critical factor in deciding when to stop or when to keep going and still make it through an intersection legally. If red-light cameras do come screeching into the Lehigh Valley (possibly as early as next year), motorists who "run" red lights won't necessarily know about it till they receive a citation in the mail some weeks later. It's important to understand the rules (some of which we discussed with police officials in the Dec. 5 column, which is viewable at mcall.com).
Could PennDOT or municipal traffic intentionally shorten the yellow-light time without justification in terms of safety or traffic-flow efficiency, but rather in an effort to snag motorists and thus raise revenue?
That should not be the case for a number of reasons. First, it's explicitly forbidden in the proposed legislation (though it might be difficult to prove that a municipal official tweaked a yellow light, particularly for this reason). The legislation also limits the municipalities' share of the money derived from citation fines and costs.
In addition, Walter said yellow-signal duration normally falls within accepted limits of 3 to 5 seconds. In fact, with the newer, electronic signal controllers, a minimum time of 3 seconds "is an industry standard built into all the … controllers" such that the yellow time should never fall below that value, Walter wrote in an email. The "yellow change interval" (engineer-speak for yellow-signal duration) is calculated based on vehicle speed, motorist reaction time (generally one second), grade of the roadway and stopping distance.
PennDOT's "Traffic Signal Design Handbook," available on the Internet, puts it this way: "A yellow change interval should have a duration of approximately 3 to 6 seconds. The longer intervals should be reserved for use on approaches with higher speeds. Excessively long change intervals may result in abnormal running of the change and clearance intervals."
The last sentence seems to suggest that if the yellow stays on too long, people might be unduly tempted to continue through the intersection, possibly blowing through the red light. It stands to reason that unduly short durations also would tend to promote red-light running — the motorist hasn't a reasonable chance of reacting in time. But that's why the standard parameters are established; 3 to 6 seconds should be reasonable. (In tables provided as examples of change intervals, the Handbook lists some intervals shorter than 3 seconds, down to as low as 2.2 seconds, as well as intervals longer than 6 seconds, up to 7.3 seconds, all depending upon traffic and roadway conditions. But again, the newer lights are pre-set at a minimum of 3 seconds.)
I timed the change intervals at Hamilton and Lincoln at 3 seconds for Lincoln traffic and 4 seconds for motorists on the main road, Alan. Purely from my perspective as a motorist, the Lincoln duration did seem a bit short — both of them did, actually — but they do fall within the recommended specs.
At the end of the road, it seems that long-established yellow-light times of between 3 and 6 seconds are reasonable, so long as they properly reflect the prevailing traffic speeds and other variables. The only difference in the debate regarding red-light cameras is over the enforcement method.
Red-light camera systems have developed deep potholes in some cities, including Los Angeles, where the city decided to shutter its program in July after courts ruled that camera citations are unenforceable, according to the Los Angeles Times.
But in closer-to-home Philadelphia, the program seems to be riding on a fairly smooth road, and a state highway-funding commission recommended this year that the option of using the cameras be extended to municipalities across the commonwealth. I'll still hitch my trailer to that tractor, and we'll see where it takes us.
Road Warrior appears Mondays and Fridays, and the Warrior blogs at mcall.com. Email questions about roadways, traffic and transportation, with your name and the municipality where you live, to hartzell@mcall.com, or write to Road Warrior, Box 1260, Allentown, PA 18105-1260.
