<P> Some cities, notably Seattle, have devised means to improve a street's retention capacity . However, frequent intersections as they occur in a regular grid would pose an obstacle to their effective application . </P> <P> A street network pattern can affect the production of pollutants by the amount of car travel that it necessitates and the speed at which cars can travel . The grid plan with its frequent intersections may displace a portion of the local car trips with walking or biking due to the directness of route that it offers to pedestrians . But it also makes the same routes more direct for cars, which could be an enticement for driving . The potential car trip displacement would result in a reduction of pollutant emissions . The advantage of the intersection density for pedestrians, however, can have a contrary effect for cars due to its potential for reducing speeds . Low speeds below 20 mph have a significantly higher coefficient of pollutant production than above 30, though the coefficient after leveling off tends to increase gradually after 50 mph . This effect is accentuated with high traffic density in areas with commercial uses where speeds come to a crawl . Since the grid plan is non-hierarchical and intersections are frequent, all streets can be subject to this potential reduction of average speeds, leading to a high production of pollutants . Greenhouse and noxious gases can be detrimental to the environment and to resident health . </P> <P> In his seminal study (1982) on livable streets that was conducted in neighbourhoods with a grid, Donald Appleyard showed that social networking and street playing degraded as traffic increased on a street . His research provided the groundwork for traffic calming and for several initiatives such as living streets and Home Zones, all of which are aimed at improving a street's social milieu . The amount of traffic on a street depends on variables such as the population density of the neighbourhood, car ownership and its proximity to commercial, institutional or recreational edifices . Most importantly, however, it depends on whether a street is or could become a through road to a destination . As a through road, it could sustain unpredictable levels of traffic that may fluctuate during the day and increase over time . </P> <P> A key characteristic of the grid pattern is that any and all streets are equally accessible to traffic (non-hierarchical) and could be chosen at will as alternative routes to a destination . Cut - through driving, or shortcutting, has been resisted by residents . Cities responded by making modifications to prevent it . Current recommended design practice suggests the use of 3 - way intersections to alleviate it . </P>

Who invented the grid system of planned cities