Learning to Love Your Traffic Engineer ? Standards

Wednesday, December 11 by JerryFoster

Using Desired Operating SpeedTo learn to love our traffic engineers, we have to understand why they don?t feel they have the authority to design roads to meet citizens? needs ? the standards won?t let them.

Marohn notes that standards are ?the engineering profession’s version of defensive medicine.?

Gary Toth invites us to ?marvel at how thoroughly the transportation establishment delivered on its perceived mandate?, including ??language/terminology; funding mechanisms; curriculum at universities; values; and policies. Common professional organizations? reinforce and standardize this? at a scale that has rarely been matched by any other profession.?

Citizens should note that engineers are required to follow the standards for traffic signals (Manual for Uniform Traffic Control Devices) – the others are guidelines.

Toth advises ?Design manuals often present standards in ranges from minimum to desirable. Has the designer selected the desirables instead of minimums?? Residents will want the minimums, as the ?desirables? are from the point of view of creating a wider, straighter and faster roadway.

Conventional DesignIn this series, we?ve set up a ?straw man? based on traditional engineering practices. The critique reported here comes from within the profession, however, and context sensitive standards such as NJDOT?s Smart Transportation Guidebook have been published that, if implemented, will significantly improve livability, which is the goal of the WWBPA.

We?ve seen how standards? flexibility enable engineers to design bike and walk friendly roadways, so in our next installment, we?ll look at liability concerns.

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Learning to Love Your Traffic Engineer – Safety

Wednesday, November 27 by JerryFoster

Rt 571 Concept Illustration

Rt 571 Concept Illustration

Not only do traffic engineers prioritize safety lower than residents, the designs that supposedly increase safety cause more death and destruction. Why? Because motorists behave differently than engineers expect.

In 2012, there were 33,561 traffic fatalities, including 4743 pedestrians and 726 cyclists.

Traffic engineers? safety improvements include paving wider lanes and shoulders, removing roadside trees, straightening tight curves, etc.? According to AASHTO standards, ?every effort should be made to use as high a design speed as practical to attain a desired degree of safety.?

Traffic engineers believe that designing for high speed will provide safety.

The crash data, however, show ?wider lanes and shoulders were associated with statistically significant increases in crash frequencies.?

Noland reports that traditional ?road ?safety improvements? actually lead to ? increases in total fatalities and injuries,? because ?this type of approach tends to ignore behavioural reactions to safety improvements?.

Dumbaugh reports that ?a behavior-based understanding of safety performance is supported by research and literature in the field of psychology, which has focused on the subject of traffic safety as a means for understanding how individuals adapt their behavior to perceived risks and hazards.?

Marohn calls the traditional approach to safety ?professional malpractice?.

Despite WWBPA recommendations, the design for Rt 571 in downtown West Windsor follows the traditional approach – 45mph design speed, another lane and wide shoulders – all in the name of bicycle and pedestrian safety.

We?ve seen that traffic engineers might improve safety by becoming better social scientists. Before following that, however, our next installment of Learning to Love Your Traffic Engineer will look at cost.

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AASHTO Takes Aim at Bike/Ped Regulations

Tuesday, April 19 by JerryFoster

The Association of American State Highway and Transportation Officials (AASHTO) recently published a letter to the US Department of Transportation recommending weakening the federal requirement for adding bicycle and pedestrian facilities to roadway projects. This recommendation is understandable, given the fierce fight for resources in today’s tight budget climate, but extremely short-sighted.

Some background: the Highway Trust Fund, established in the 1950s to finance the interstate highway system, has suffered from starvation due to flat fuel taxes (since 1997), reduced buying power of those taxes through inflation, and fewer miles driven since 2007? (i.e. reduced demand for gas) due to the economy, more fuel-efficient cars and higher gas prices. Intended as a way for motorists to pay for highways, it has been bailed out by general taxes to the tune of $8 billion in 2008, $7 billion in 2009, $19.5 billion in 2010, and is projected to be insolvent again by the end of fiscal year 2012.

However, the percentage of federal roadway money spent on bicycle and pedestrian facilities is minuscule (about 2% in FY 2010), and a sustained commitment is necessary to build our transportation network to offer a true choice of modes – walking, biking, transit and/or driving. It’s a win-win in any case: better walking and biking facilities are usually incidental to the cost of building roads or bridges, they’re healthier for the participants, plus they reduce congestion and pollution for everyone.

Consider this picture, which I took while walking the 1.5 miles from the commuter train station near Frederick, MD to pick up my car at the dealer (don’t ask). This bridge, MD 85 under I-270, appeared to be recently constructed and had a number of nice features, such as the stone work shown, and should have been built with room to walk, but wasn’t.

Please use this link to express your opinion of whether bicycle and pedestrian facilities should be required, or just considered.

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Roadways Designed for Speeding?

Friday, November 5 by JerryFoster

Cars Don't Want to Stop from 40mphAccording to NJDOT’s Smart Transportation Guidebook, many different factors come into play when choosing a desired operating speed for a roadway. From the discussion of speed:

“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.”

According to the Rt 571 Concept Design reviewed by county engineers in December 2009, the Main Street Princeton Junction design speed is 45mph, posted speed is 40mph, keeping the same values as exist currently.

Vehicle speed affects pedestrians’ safety in a number of different ways.

Likelihood of Collision

?Faster speeds increase the likelihood of a pedestrian being hit,? according to Federal Highway Administration’s Pedestrian and Bicycle Information Center.

Severity of Collision

If a pedestrian is hit by a vehicle traveling at 40mph, he/she has a 15% chance of survival, but if the vehicle is going 30mph, chance of survival increases to 55%, according to the Federal Highway Administration’s Pedestrian Facilities Users Guide: Providing Safety and Mobility (2002).

Crosswalk Compliance

Last, motorist compliance with yielding to pedestrians in crosswalks is significantly improved by reducing vehicle speed to below 35mph, according to the federal report Improving Pedestrian Safety at Unsignalized Crossings.

The WWBPA has requested the township to work with the county to follow the new NJDOT approach (called Context Sensitive Design) to choosing a desired operating speed, to support our emerging Main Street. NJDOT guidelines for a Community Arterial in a Suburban Center or Town Center context call for a desired operating speed of 25 – 30mph. Please support the WWBPA by contacting our officials, or write us an email at wwbikeped@gmail.com.

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AASHTO Recognizes Livable Communities

Wednesday, May 5 by JerryFoster

The American Association of State Highway and Transportation Officials just published a guide to Livable Communities that included PennDOT’s use of the Smart Transportation Guidebook, which was developed with NJDOT and is a primary resource in the WWBPA’s recommendations for downtown Princeton Junction.

“Through a program called ?Smart Transportation,? Pennsylvania has been working to find innovative solutions to the challenges of constrained resources, aging highways and bridges, and congestion by reexamining the relationship between land use and transportation. One example is PennDOT?s U.S. Route 202 Parkway project in suburban Philadelphia. First envisioned as a new four-lane expressway between Doylestown and Montgomeryville, the project?s cost was simply not affordable. After an extensive consensus-building process, a lower-cost option to build a parkway-type design was approved at roughly half the original cost. The new Parkway included a 12-foot wide bicycle and walking path along its entire 8.4-mile length; concrete stamped , and painted to simulate the appearance of stone on all bridges, culverts, and retaining walls; and landscaped median strips and other aesthetic enhancements.

The Parkway will be built as four lanes for two miles and two lanes for six miles and speed limits will be lowered. Nine signalized intersections will replace three interchanges and slower speeds will help increase safety.”

There is also a section on Main Streets in the document, which can be found at:
http://downloads.transportation.org/LR-1.pdf

AASHTO is traditionally very motor-vehicle-oriented, so for them to recognize the role of context sensitive roadway design in making our communities more livable is a welcome sign of improvement.

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