Adams St., as I described in a previous post, is a very 20th Century design.

I’ve got nothing against 20th Century traffic engineers. They were, undoubtedly, fine, god-fearing, family-loving men deeply committed to contributing to the common good through their chosen profession. But, holy cut-through, Batman, they were monomaniacal in their focus on promoting vehicle movement.

There’s a reason the Complete Streets movement arose. Cities built around the private automobile turn out not to be terribly safe or pleasant places to live. It’s why Newton is officially committed to a Complete Streets policy, which means roadway design that shifts the focus to include and foster other modes of travel: walking, biking, mass transit.

So, how could/would/should Adams St.be different in a 21st Century, Complete Streets design?

It might not be so straight. It might have shorter, safer pedestrian crossings. It might have first-class bike accommodations. It might have elements designed to slow motor vehicle traffic.

There’s a mix of design solutions available. How you mix and match depends on money and what you’re optimizing for. What follows is in no particular order.

It’s axiomatic that making traffic turn slows traffic. It’s called horizontal deflection. On an existing street like Adams St., you could add a chicane.

For the length of the chicane, everything shifts 6-10 feet, except one side of parking. Remove parking on the west side, shift the two travel lanes and the east side parking, and add to the grass berm or the sidewalk on the east side. Cars traveling south turn a little right into the chicane and a little left out of the chicane. Cars traveling north turn a little left into the chicane and a little right out of the chicane.

Cambridge uses chicanes for some of the cut-throughs connecting Brattle St., Mount Auburn St., and Memorial Dr.

It is also axiomatic that the less time a pedestrian spends in the street, the less opportunity there is for car v. pedestrian conflict. At crossings, this means shortening the length of the crosswalk. One straightforward intervention is to reduce curb radii. As I discussed previously, the shorter the curb radii, the tighter the corner, which reduces the distance between corners.

The city could — and should — tighten the curb radii on every corner on every re-paving project. It adds cost, but during a repaving project is the cheapest time to do it. Actually, in some cases, it doesn’t add construction cost. Sometimes the city has to replace curbing and replaces it with the original design, when tightening is warranted.

Adams St. has over 20 corners. Tightening the radii on each would reduce the time pedestrians spend in the street. As important as the actually increase in safety is the perception of increased safety. Keeping pedestrians out of the street encourages people to walk.

A side benefit of shorter curb radius is that a tighter turn discourages speed through the turn. Put another way, a longer curb radius encourages faster speed through turn. The long curb radii on Adams St. are artifacts of a very car-centric design.

Another mechanism to reduce pedestrian time in the street is a curb extension. 

The width of Adams St. — 38-1/2 feet — allows for two lanes of parking and two motor vehicle travel lanes. For travel across Adams St., the distance is 38-1/2 feet. The Manual of Uniform Traffic Control Devices specifies an average walk speed of 4 feet/sec. Seniors require more time. 

A curb extension is a little peninsula of sidewalk that extends across the parking area up to the travel lane. Curb extensions on both sides of the street can cut the crossing distance by more than a third. Also important, curb extensions gives someone wanting to cross the street better visibility — pedestrians see vehicles better, drivers see pedestrians better. The city has installed curb extensions at several locations. Newton Centre has a couple on Centre St.

There’s one particular use case where curb extensions make a big difference. People don’t like to step into the street until the coast is clear. This is noticeable even when a parked car — before and/or after the pedestrian — gives a pedestrian cover. The effective crossing distance is shorter by the width of the car(s), but pedestrians rarely use the cover of the car(s) to step out and actually shorten the crossing. With a curb extension, the pedestrian can get past (or nearly past) the parked car(s) from the safety of the sidewalk.

Curb extensions also shape driver behavior. They narrow the street, at least a bit, which naturally slows traffic. And, they signal that it’s a pedestrian-likely zone better than a crosswalk on its own.

The next step up (pun not intended, but not edited out, either) from a curb extension is a raised crosswalk or speed table.

A raised crosswalk literally extends the curb extension all the way across the street. It provides a safe crossing, in large part because traffic has to slow to get over it. Depending on design and car, speeds could slow to as little as 15 MPH, which makes it much, much safer for pedestrians. (More time to react and less mortality if there’s conflict.)

Where should/could the city have put curb extensions or raised crosswalks across Adams St.? The intersections at Washington St. and Watertown St. are obvious candidates. There was a crossing striped at Lincoln Rd./Middle St. and would be something to look at. I rely on someone who knows Adams St. more intimately to suggest others. 

Adams has so much pedestrian activity and opportunity, it probably isn’t a good candidate for speed humps, another tool in the Complete Streets toolkit. Better to have raised crossswalks, which are really just a version of a speed hump.

What about the bikes, you ask? Simply slowing traffic on Adams would make things better for bikes. See the options above. Removing parking from one side or the other would create room for bike lanes. Better yet, create grade-separated cycle tracks on both sides, which would have the additional benefits of narrowing the street and providing a buffer between pedestrians and traffic. Bike lanes don’t have to go straight, they can be combined with chicanes.

A relatively minor issue, but most easily done: rebuild the corners with separate ramps directed straight across the cross street and, if necessary, straight across Adams.

Sadly, lots of foregone options on Adams St.

Next up: why does the city keep blowing these opportunities?







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