Penn Pike Whip Interchange on NE Extension at MP87/PA903 to cost $25m (ADDS)

The Pennsylvania Turnpike Commission has announced details of the new interchange it's building on the Northeast Extension (I-476) in the Pocono Mountains at PA903 near Penn Forest Township/Albrightsville, seat of House Majority Whip Keith McCall. The interchange at Mile Post 87 is well located to link with an existing county road that presently crosses it without any connections in a long 31km (19 mile) stretch between Pocono IC95 at I-80 and Mahoning Valley IC74 (misnumbered, it should be IC76 because it's near MP76).

Earlier report with general location maps

http://www.tollroadsnews.com/node/3792

The all-electronic interchange will have transponder and video equipment on all four ramps of a diamond style interchange, which saves on land and paving as compared with the trumpets needed to bring four directions of traffic together on a full service manual toll collection plaza which was standard on the Turnpike before electronic tolling.

This is only the second new interchange to be built on the NE Extensions since it opened in the 1960s.

The Turnpike says "the new facility will shorten travel times for commuters; help ease traffic congestion at neighboring interchanges and on local roads; and provide additional access to nearby recreational areas."

Cost is estimated at $25m and the Turnpike wants to begin construction within a year (fall 2009) for opening in fall 2011. First stage will be a new wider overbridge needed for storing traffic at the two sets of signals at the top of ramps each side. That is planned to open May 2010, after which the ramps will be built. Environmental approval should be straightforward given the strong local support and minor encroachment on nearby properties.

The nearby area has more than doubled in population from about 2,900 people in 1990 to about 6,500 now, based on its attraction for retirement and recreation. The interchange was first proposed in 1985 but the Turnpike said traffic wasn't sufficient. More recently there was discussion of south-facing ramps only. But even though the north facing ramps will attract less usage - interchanges at I-80 serve that traffic reasonably  better than IC74 serves the area - complete interchanges serving all traffic movements make for easier signing and maps, and less motorist confusion.

For the moment they talk of the interchange being E-ZPass (transponder) Only but it seems likely by the time it is opened that will be amended to allow video tolling for those without a transponder.

Turnpike CEO Joe Brimmmeier is quoted as saying the Turnpike is not going to build any new toll facilities with cash. All will be electronic-only like this in future, the policy of most tollroads in the US now.

COMMENT: Designed to give political pork a good name - McCall was an outstanding defender of the Turnpike Commission against Governor Rendell's plan to privatize it - the IC87 interchange looks to be well justified as a project.

31km (19 miles) is way too long a distance between interchanges (IC74 at MP76 and IC95), and development in the area nearby calls for improved connections to the Turnpike like this.

There should be a lot more of these now that interchanges can be built without the expense of manual toll booths and the need to bring the different directions of traffic together with a trumpet design.

However, $25m seems a lot of money however to pay for four simple ramps, some road and bridge widening, signals and electronic toll gear.

BAD DESIGN: Also this is a rotten, obsolete design - poor traffic engineering. Signals should not be used on low volume, high speed rural highways like this. The greens invite traffic to accelerate to get through before the red, and the low volumes of traffic encourage risktaking through the yellow and the early seconds of the red.

Second, some sight lines are terrible at these top-of-the-ramp intersections because of the angle at which PA903 crosses the turnpike. Motorists southbound off the Turnpike heading east on PA903 and traffic off the turnpike northbound heading west will have to look left at about 130 degrees to check against cross traffic.

Predictable result of this design: a high incidence of cruel sideswipe collisions, many fatal over the years.

The correct treatment is twin roundabouts - one on each side of the overbridge. The roundabouts force all traffic to slow to safe speeds for giving way and merging without stopping anyone. The twin-roundabout design also reduces the width of bridgework needed because traffic keeps moving and clears the intersections faster than the twin signals arrangement. There's no need to store turning and waiting traffic on an expensive six lane structure on top of the mainline if roundabouts keep traffic moving steadily through on each end.

Kansas Turnpike and many other state highway departments and toll authorities are doing twin-roundabout designs at interchanges like this.  They are proven to save lives, time, fuel and construction cost compared to these dangerous signalized intersections.

EXPERT COMMENT: A partner in a major leading transportation consulting firm comments: "I agree with your proposal.  Roundabouts at ramp terminals are a great idea particularly when the cross road is not a high volume high mobility route itself.  If the main purpose of this interchange is to provide access to the turnpike, and it reads like it is, then the roundabouts make perfect sense. 

"In addition to your comment about bridge width (not needing turn lanes with the roundabouts) is very true.  It may be also possible with roundabouts to "square up" the bridge to shorten it as well.

"However, your sample picture shows an interchange where the frontage roads are combined with the ramps at the roundabouts.  While this has been done at a number of places (Vail Colorado and Cottage Grove Minnesota) it doesn't look like its would be needed at your subject location.  The FHWA has told us that they do not like using "their" ramp intersections to complete the local roadway system.  As a result, Wisconsin typically installs separate roundabouts for the frontage road junctions.

"Unfortunately another logical reason for using roundabouts at diamond interchanges is that very few traffic engineers today know how to properly design and operate the signal systems needed for efficient diamond interchange operation.  This is the reason single point interchanges have become so popular.

"Your buddies at the state of Maryland have installed roundabouts at several ramp intersections in Howard County (on the MD100 expressway).

"There is another benefit with roundabouts that we are exploring at a proposed interchange in Minnesota and that is that the possible spacing of the frontage road and ramp intersections is more flexible with the use of roundabouts.  If signal control is assumed, MnDOT and the county want 1000 feet minimum to the frontage road intersections and 800 feet between the ramp intersections.  For a total distance of 2800 feet plus approaches.  If roundabouts are used the spacing would be 600 feet between roundabouts for a total distance of 1800 feet.  So the impacted area would be smaller and the roundabout locations could readily be adjusted to fit desired parcel sizes for possible development (on PA903).

EDITOR: here are pictures of twin roundabout interchanges from Brisbane Australia and, closeby, here in Maryland (MD100/MD103 in Howard County) that are more in the style needed at I-476/PA903.

Please someone: defend the old diamond.

http://www.tfhrc.gov/safety/00-0678.pdf

TOLLROADSnews 2008-10-25  ADDITION: 2008-10-27:18:30