Q: I have often wondered who decided on the lane arrows when you turn from Hamilton Boulevard onto Mill Creek Road south— toward Walmart. At the intersection created by the Walmart entrance/exit, it seems to me the right lane should be for right turns and through-traffic, since those vehicles will keep moving. The left lane should be for left turns only. The actual design is just the opposite, which seems illogical. Anyone who has come in the northbound direction, from Lower Macungie Road toward Hamilton Boulevard, will know what I mean, as it's always an adventure trying to get across the intersection. What do you think? Makes more sense to repaint the arrows?
— Tom Weiss, Emmaus
A: I think you're absolutely right, Tom. Your proposal would seem to improve traffic flow, particularly on northbound Mill Creek Road, without sacrifice in terms of safety or flow in other directions.
Before I get to PennDOT engineer Tom Walter's take on why a private design engineer might have chosen the existing configuration (PennDOT did not design the intersection), I'll map a course to my rationale as to why the right lane should be marked for right turns and through-traffic, and the left lane designated for left turns exclusively, exactly as you suggest.
Traffic turning right at this intersection goes to one place only: the church adjacent to the shopping center. It's a big, popular church with a sprawling parking lot, but it's merely one destination that can't possibly generate the kind of traffic volume of a Walmart Supercenter. Not even on Sunday mornings.
The left turn into Walmart would seem the prevailing movement by far, so it would make sense to dedicate a lane to that traffic exclusively. Right-turning and through traffic, likely of lesser volume even combined, could afford to share the right lane.
Keeping in mind that southbound traffic has no stop sign (stops are posted in the three other directions), your design, Tom — our design — would solve a problem for the oncoming northbound traffic at the intersection. Currently, northbound motorists can't know for sure whether opposing traffic in the left-turn/through lane will turn left or go straight. They should be able to tell, based on turn-signal use, but in practice, that's about as reliable as state transportation funding. If a defendant serving as his own lawyer has a fool for a client, a motorist trusting turn signals also qualifies.
So under the current design, northbound motorists can be held up, unnecessarily, waiting for traffic they think might be turning left in front of them, but actually is going straight and would not pose a conflict. This could be happening often enough to produce northbound queues, especially at times of heavy traffic.
In our design, northbound motorists would have a much better idea of the intentions of motorists coming the other way, based on which lane they are in. Southbound motorists turning left into Walmart almost always would be in the left lane. Everyone else should pose no conflict with northbound travel, freeing the latter for more efficient movement through the intersection and onto Hamilton Boulevard. True, motorists' intentions could not be fully trusted based on lane position, but it would be more reliable than turn signals alone.
Walter allowed that those considerations are legitimate and could be part of the mix when considering intersection designs. So we're not totally off the road and into the weeds, Tom. However, Walter said our design might complicate the traffic pattern from behind, as it were, on the southbound stretch of Mill Creek from Hamilton to the intersection.
Under our design, all southbound traffic from Hamilton Boulevard onto Mill Creek Road not intending to turn left into Walmart "would have to weave/merge into the right lane" in the short distance between Hamilton and our intersection, to continue south or to turn right into the church, Walter said. These drivers "would have to compete with one another in such a short distance," jacking up the conflict potential, he said.
Challenging weave patterns surely should be avoided when possible — I can't help but think of the horrific conditions on the northbound Route 222 Bypass from the Hamilton Boulevard intersection to the I-78 interchange — but I don't think the Walmart weave would be any worse, or better, under our design versus the current one. The two inbound lanes from Hamilton are divided by a concrete island, and then by road marking, to keep traffic separated. It's only about 300 feet from the end of the marking to the intersection, and Walter is right: Any weaving has to happen in that distance. But I see no difference in conflict potential between weaving from left to right or right to left. It might be a little tricky, but it's the same level of challenge either way.
Walter added that the right-hand curve in southbound Mill Creek Road through our intersection also would weigh in favor of maintaining the existing turn-lane design, simply because through motorists intuitively would tend to follow the natural curvature of the road. OK, but that's a minor factor. I don't think it overtakes the advantages of our design.
Walter didn't convince me that the chosen design is superior to ours, Tom, and for that matter, he wasn't necessarily saying it is. He simply reviewed some of the factors that normally would be considered in designing an intersection such as this.
As I've found in other questions about intersection functioning and other traffic issues, for all its legendary precision, engineering often isn't an exact science. A gain in traffic-flow efficiency might be offset by safety concerns, or a specified goal could be dropped because of difficult topography, or (more likely) cost restrictions.
Do engineers get it right every time? Does anyone?
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