Q: I am perplexed by how the 'right turn on red' prohibition is applied at different intersections. In East Allen Township, Snowdrift Road joins Airport Road at an oblique angle, opposite Hanoverville Road. Drivers on Snowdrift stopped at the light at Airport routinely turn right on red. I think right on red should be prohibited.

Edwin Kay, Bethlehem

Q: Why aren't right turns on red allowed from Dauphin Street onto Union Boulevard in Allentown? There's plenty of sight-distance. I think it would be perfectly safe, and traffic would move along more efficiently.

Paul Kershner, South Whitehall Township

A: Traffic engineers determine whether right turns on red are allowed at signalized intersections. Guidelines apply, but conditions at no two intersections are exactly alike, and interpretation plays a main-road role in deciding where to post "no turn on red" signs, and where to let traffic flow more freely. In cases where the ban is in effect and the reasons for that seem unclear, engineers likely decided to err on the side of caution, theoretically favoring motorist and pedestrian safety. On the other side of the road, the demands of efficient traffic flow should get due consideration.

According to the Manual on Uniform Traffic Control Devices, a kind of road map for U.S. traffic engineers, "no turn on red' should be considered when one or more of the following conditions exists:

"Inadequate sight distance to vehicles approaching from the left (or right, if applicable); geometrics or operational characteristics of the intersection that might result in unexpected conflicts; an exclusive pedestrian phase; an unacceptable number of pedestrian conflicts with right-turn-on-red maneuvers, especially involving children, older pedestrians, or persons with disabilities; more than three right-turn-on-red accidents reported in a 12-month period for the articular approach, or the skew angle of the intersecting roadways creates difficulty for drivers to see traffic approaching from their left."

Some of these are wide-open highways to interpretation ("unacceptable" number of pedestrian conflicts), and note that the manual says the ban "should be considered," not "shall be imposed." At the end of the road, it's largely a judgment call.

Properly executed right turns on red are allowed in Pennsylvania in the absence of "no turn on red" or "no turns" signs. The law first requires a complete stop, and yielding to conflicting vehicular or pedestrian traffic. Left-on-red is allowed if both streets are one-way streets. And it's strictly optional: Drivers can refuse to make the turn for any reason, including merely to aggravate the impatient motorists behind them. (That may not be polite, but it is perfectly legal.)

The intersection of Airport Road with Snowdrift and Hanoverville roads is a model so rare it's suitable for collectors. As you pointed out in your email, Edwin, it features traffic-signal heads mounted on the same cross-member but facing in different directions to control different streams of traffic. For motorists on Snowdrift facing Airport, the signal heads on the arm to the right, but angled toward Snowdrift, work in concert with those across Airport; the angled heads are auxiliaries, more easily viewed by right-turners. Motorists crossing to Hanover tend to maneuver their vehicles to face Hanover, and thus face the signals across the way. It's unusual.

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Right-on-red postings: Right or wrong?