Re: Converting a cloverleaf to a diamond interchange?

hancock4@xxxxxxxxxxxx wrote:

I drove through the interchange between PA Rt 309 and Easton Rd in
Glenside PA, just outside of Philadelphia. There used to be a weird
cloverleaf there which has been replaced by a simple diamond and a
traffic light during a major upgrade project on Rt 309.

I thought the idea of improving an interchange was to go cloverleaf
instead of a diamond to avoid the need to cross the side road, so I'm
surprised they went this route. The only thing I can think of is that
the old ramp entered Rt 309 on the left side of the highway making the
merge more difficult since it was into the passing lane. The new
layout is certainly simpler.

The usual treatment is to remove one of the two loops that cause a
weaving section on the high speed highway, and shift the traffic onto
the ramp with a traffic signal on the crossing road. A cloverleaf
interchange, while it is more efficient on the crossing road than a
diamond or other type, creates trouble on the main road with those
short weaving sections. They work until traffic gets heavy on the
freeway, then removing one or both loops is done.

John Lansford, PE
--
John's Shop of Wood
http://wood.jlansford.net/
.

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