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A ROUNDABOUT WAY

Traffic calming devices touted as air quality pluses

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A ROUNDABOUT WAY

The city expects bulb-outs at intersections such as these on Maple Avenue in downtown Manteca will increase walking by slowing down traffic making it safer for pedestrians and therefore reduce carb...

DENNIS WYATT/The Bulletin


POSTED March 20, 2013 1:16 a.m.

Bulb-outs - the much maligned landscaping devices that jut out into street parking areas in downtown Manteca - are going to become a staple of new neighborhoods.

And it’s because state air quality gurus believe aggressively deployed traffic calming devices that also includes roundabouts can reduce greenhouse emissions by 0.25 to 1 percent. Traffic calming devices are seen as a way to increase walking and bicycling. In the case of roundabouts, they also reduce vehicle stop and go movements at intersections that would traditionally have had stop signs installed. Acceleration and idling causes a surge in vehicle emissions.

Bulb-outs and roundabouts are part of an arsenal of design tools for new development the city hopes will allow it to meet emissions reductions mandated by Assembly Bill 32 known as The Global Warming Solutions Act signed into law in 2006. Manteca has to find ways to impose development policies and other strategies that will reduce projected carbon dioxide emissions based on growth, current pollution levels and state-imposed changes in 2020 by an additional 12,014 metric tons a year.

The administrative draft of Manteca’s climate action plan also points to making lanes narrower than the current 12-foot standard for streets to slow traffic, make it easier for pedestrians to cross streets and improve bicycling comfort. The only exception would be on streets that have other safety issues such as truck routes. In such cases, the narrower lane design would not apply to outside lanes where trucks travel.

Narrower travel lanes - especially in residential developments - would help reduce the cost of infrastructure and long-term maintenance by cutting back on the expanse of asphalt. Theoretically, it could also reduce emissions as the construction process also is being forced to comply with greenhouse gas reduction. The less street pavement means fewer emissions created through the mining and transport of materials and mixing of asphalt as well as the use of equipment to construct streets. All of that activity figured into the 408,869 metric tons of carbon dioxide equivalents the state said the Manteca community as a whole generated in 2010.

Besides bulb-outs at appropriate intersections in new neighborhoods to reduce crossing distances and calm traffic, the city will start requiring marked mid-block crossings near schools, parks and “other neighborhood attractions”. The mid-block crossing could include a landscaped median refuge island or a raised or textured sidewalk. In some cases, signals may be required depending on traffic volume.

As for those downtown bulb-outs, the climate action plan calls for more of them along Main Street, Yosemite Avenue and other high use areas. But they wouldn’t be as much for landscaping purposes as most existing bulb outs are downtown. Instead, they would be more like the ones on the north side of West Yosemite Avenue at Maple Avenue where the bulb-outs reduce the street crossing distance for pedestrians.

Also to encourage people to get out of their cars for shorter trips, the plan calls for wider sidewalks where possible, buffers between sidewalks and vehicle travel lanes, providing benches, and allow for cafe seating.

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