Slow Down in Plainsboro

Wicoff School, PlainsboroResidents around Wicoff School in Plainsboro want police to strictly enforce the 35 mph speed limit and the 25 mph limit during school hours or that the speed limits be reduced, and both the police chief and mayor say they understand. Police have issued 59 tickets in the area over the past year, or a bit more than one a week.

But here’s some insight into how hard it can be to change a speed limit and how much we tolerate breaking the speed limit: According to an an article in The Packet, a police traffic survey done this summer found that about 90% of cars were traveling at 40 mph, with the remainder traveling above 40 mph. Under New Jersey Department of Transportation’s regulations, this isn’t a problem because at least 85% of cars are traveling within 5 mph of the speed limit.

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3 Responses to “Slow Down in Plainsboro”

  1. Brian says:

    “Therefore, this
    guidebook recommends that the desired operating speed for most roadway types be the same as the design speed, and also the same as the posted speed.”

    Spot on. Not doing so obviously decreases traffic flow, and therefore safety. However, the idea that indiscriminately lower speed limits are safer is so heavily in our collective conscience that it is difficult for people to get past the idea. Engineers need to also consider differences in vehicle safety and mechanics when determining operating speed, as vehicles have evolved considerably in the last 30-40 years. A family V6 sedan can accelerate, handle, and brake better than most exotic cars from 1975.

  2. Jerry says:

    Thanks for commenting again on our site – I meant to reply to your previous comment re: the 85th percentile rule earlier. This information all comes from NJDOT’s Smart Transportation Guidebook, published March 2008.

    Context Sensitive Design

    “Roadways should respect the character of the community,and its current and planned land uses. If appropriately designed, vehicular speeds should fit local context. The concept of desired operating speed is key to the context sensitive roadway.”

    Design Elements

    Three kinds of design elements are described:
    “Desired Operating Speed: This is the speed at which it is intended that vehicles travel.”
    “Roadway: The design team should select roadway elements and geometry with a clear understanding of surrounding land uses.”
    “Roadside: The roadside primarily serves the pedestrian and the transit rider and provides a transition between public and private space.”

    Land Use Context

    The Guidebook describes 7 land use contexts – Rural, Suburban Neighborhood, Suburban Corridor, Suburban Center, Town/Village Neighborhood, Town Center, and Urban Core.

    Roadway Categories

    Overlaying traditional functional categories, the guidebook describes a typology “which better captures the role of the roadway within the community.” These categories are Regional Arterial, Community Arterial, Community Collector, Neighborhood Collector and Local.

    “‘Main Street’ is an overlay of the Community Arterial or Community Collector road type. The design of a Main Street is taken from the elements of those road types within the Town Center or Urban Core contexts.”

    Matrices are provided which describe the appropriate design standards for each type of roadway and land use context.

    Speed (long quote):

    “Desired operating speed is best explained by its relationship to three other concepts of speed: operating speed, posted speed, and design speed.

    Operating speed is the speed at which a typical vehicle operates, commonly measured as the 85th percentile speed of all vehicles.

    Posted speed is the legal speed limit on a roadway. It is often set without any means of self enforcement, and drivers tend to travel at what they perceive as a safe speed regardless of the posted speed. Fewer than a third of drivers go the speed limit on urban and suburban arterials.

    Design speed (as defined in the AASHTO Green Book) is the speed used to determine various geometric design features, including horizontal curvature,
    gradient, superelevation, stopping sight distance, and, for rural highways only, lane width.

    Historically, New Jersey has required the design speed to be 5 mph above posted speed for existing roadways, and 10 mph for new roads.

    The greatest drawback to the existing design speed approach is that drivers usually drive as fast as they believe the road can safely accommodate. Existing policy may thus encourage operating speeds higher than the posted
    speed limit and/or selected design speed in an area. In the interest of highway safety, it is desirable to have a stronger relationship between the posted speed limit, design speed, and operating speed. Therefore, this
    guidebook recommends that the desired operating speed for most roadway types be the same as the design speed, and also the same as the posted speed.”

    Jerry

  3. Brian says:

    Well this is a surprise, I was visiting to check up on my old comments and this post was just made.

    Change the limit to 40 mph (45 past fox run) in accordance with 85th percentile rule and get the tailgaters and light violators who have the highest potential to cause accidents/hit people. I’ve biked in the area about a dozen times and seen tons of stuff, even a collision (I was in a car that time) Lowering the limit below the 85th percentile does nothing. I used to go about 35 here anyway and 40 or so on the more open section of Edgemere but we moved to Lawrence. A few crosswalk lights would help if they are not there.

    Making it 25 makes no sense because what about when children aren’t present? 25 is a small side street speed, not for a regular road. Nobody will follow arbitrarily set speed limits, and people don’t realize this (includes 55 on an interstate highway, or 50 on 133). The vast majority of people slow down when children are directly present (often to well under 25 if its packed), my friend got busted here once for 40 when there were no kids present at 7 in the morning but the cop insisted it was still 25. I rarely see people speed by when kids are actually there and the cops always enforce when there are no children present because there usually isn’t a speeding problem when there are.

    As for ‘people just go 10 over’ thats not true, we have a 40 mph limit in lawrence on 206 and except late at night in some of the more open areas most people follow it. In fact, in the tighter areas, most go 30-35.

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