Tuesday, May 29, 2007

Comm Ave. Carriage Road at Robinhood St.

An item before the Traffic Council last week presents a perfect opportunity for the kind of semi-permanent -- and cheap -- traffic calming measures that I have advocated before. In a split vote, the Traffic Council denied a request for a new stop sign at the intersection of the Commonwealth Avenue carriage road and Robinhood Street, but seemed unanimous in agreement that there was a problem at the intersection and that the problem would best be cured by a redesign.

The problem is money. While it is tempting to say that money should be no object in keeping our streets safe, the reality is that the city doesn't have the money to execute a redesign in granite curbing and new asphalt.

Rather than throw up our hands and say, "revisit the problem when the street is up to be repaved," we should rethink our aesthetic standards. This particular problem could be addressed for (well?) under $5,000 (not counting study and design).

Click through for a full description of the problems and a semi-permanent solution.

The two problems at the carriage road/Robinhood St. intersection are fairly easy to understand.

Problem 1: Lots of traffic travels west(ish) on Auburn St., then turns right onto Comm. Ave. at the light (heading northish). To beat the light (and the traffic waiting at the light), some of that traffic turns right on the carriage road, left at Robinhood St., and right onto Comm.Ave. It's a nifty little cut-through to save precious seconds, if you're willing to use the carriage road as your own personal speedway.

Problem 2: The right-of-way at the intersection of the carriage road and Robinhood St. is ill-defined. (Hence, the request for a stop sign on the carriage road.) Problem 2 is exacerbated by the cut-through traffic wanting to execute the quick left/right from the carriage road to Comm. Ave.

There are a number of solutions, all of which would have the same purpose: eliminate the benefit of the cut-through and return the carriage road to its proper uses, which include safe and comfortable walking, running, and biking.

A resident of the carriage road described how she wouldn't let her sons (8- and 10-years-old if memory serves) bike on that stretch of the carriage road. That's a civic loss that is much larger than the trivial benefit the cut-through confers on clever motorists.

One solution would be to place chicanes along the carriage road and a roundabout in the intersection of the carriage road and Robinhood street. Chicanes would physically slow traffic along the carriage road. The roundabout would eliminate the quick left-right from the carriage road to Comm. Ave., making the intersection more rational and adding more time to the cut-through. The combination should remove the advantage of the cut-through and re-route cut-through traffic back onto Comm. Ave. from Auburn St.

Done to current Newton standards, the combination of chicanes and roundabout would probably cost over $25,000 and as much as $75,000 (rough estimates). Ultimately, we'd want construction done to those standards.

But, is there something we can do in the meantime for less?

Yes. The picture of stacked-paver chicanes at the top of the post is from the front page of TrafficCalming.org. Each chicane appears to be built using about 150 pavers, which probably cost $.50 to 1.00 each. There's no nice grass fill in, just the existing pavement.

Pavers would work, but I'd recommend using 5-10 concrete curbs (like you drive up against at the end of parking spaces). Even with some signs behind either, the material costs would be under $500 per chicane. And, the installation would be very simple. Stack the pavers or nail the curbing into the pavement.

Likewise the roundabout. Consultants studying a mini-roundabout for the intersection of Daniel and Jackson street estimated the cost at $25,000 to $100,000. But, the same effect could be accomplished for probably less than $1,000 with 15-30 concrete curbs to define the roundabout and reshape the intersection, as necessary, and a handful of chevron signs inside the roundabout to alert motorists.

From experience, we know that sandbag trials of new geometry work to produce the effect of the eventual construction. Sandbags are cheap, easy-to-install, and easy-to-remove (for permanent construction, plowing season, or if the trial is unsuccessful). But, sandbags are only a short-term solution. They get run over and disintegrate (if they are not taken!).

My concrete curb proposal would give the city a step between sandbags and permanent construction. Like sandbags, they are cheap, easy-to-install, and easy-to-remove. And, they would accomplish the traffic-calming objectives. But, they last.

Installation of concrete curbs would not interfere with drainage. Concrete curbs have drainage slots on the bottom and they could be set with space between them to allow for further drainage.

Above, I qualified my own (amateur) estimate as "not counting study and design." It's an important qualifier. Even a solution rendered in cheap materials needs to be properly studied and designed. And, the city engineering staff is already spread pretty thin. But, design costs should not be a show-stopper.

In sum, concrete-curb traffic calming devices would not be as attractive as fully-realized construction, with granite curbs and grass fill-in. But, they would be plenty attractive as a medium-term solution to real traffic problems that are a lot uglier.

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