Sustainable urban mobility

The main goal of Sustainable urban mobility is to reduce the use of powered private vehicles. It focuses on sustainable travel modes, especially active mobility (walking and cycling), which is characterized by being the healthiest, least environmentally controversial, economically most rational and most socially equitable form of mobility. These advantages make active mobility “the most favourable mode in terms of sustainability” (Pucher and Buehler, 2008) while it is also supported by other modern paradigms for creating green, healthy cities that are pleasant to live in (State of Green, 2016).

Achieving a notable increase in active mobility for daily trips requires a significant improvement of the conditions for walking and cycling by establishing a system of safe, comfortable, direct and attractive infrastructure (Pucher and Buehler, 2008) and exclusive routes for pedestrians and cyclists (Banister, 2008). Comprehensive traffic calming is increasingly recognized as one of the more effective approaches. Its basic elements are larger set areas, most often in residential neighborhoods, around schools and in city centers, where pedestrians and cyclists have priority. In addition to arrangements to reduce the speed and volume of motorized traffic aiming at improving traffic safety, the interventions also include the redesign of the public open space with the aim of improving the quality of living environment and changing travel habits into more sustainable ones (Balant and Lep, 2020).

The Impact of Reducing Speed on Collisions: Decreased Numbers and Severity

Traffic calming strategies generally aim to reduce driving speeds (often to about 30 km/h), and particularly those of the fastest drivers (TDME, 2010). Consequently, strategies that succeed on this level can reduce the number and severity of collisions. Calming strategies, by helping create more complex environments, can induce drivers to pay more attention and, thus, reduce the number of collisions. The number and severity of collisions tend to increase with speed (Sergerie et al., 2005), as increasing speed decreases a driver's field of vision and increases vehicle stopping distance, two factors that decrease the likelihood of a driver being able to stop his or her vehicle in time to avoid a collision, or slow down enough to avoid a serious accident (BPA, 2008a).

Japan as an example of Success in Reducing Traffic Fatalities, but Challenges for Walking and Cycling Safety persist

Traffic accident has been a serious social problem in today's automobile-dependent society. Due to highly advanced and sophisticated road traffic system in Japan, the number of traffic accident fatalities has decreased since 1992, below falling 5000 people in 2008. In 2013, the country recorded 4373 fatalities (Cabinet Office, Government of Japan, 2014).

However, the number of fatalities during walking and bicycling has not decreased notably, whereas that of motor vehicle occupants has decreased significantly. Especially, the vulnerable road users (i.e. children under 15 years old and the elderly over 65 years old) account for almost half of all fatalities during walking and account for over one-third of all fatalities during bicycling. In addition, almost half of the fatalities for age under 15 years and over 65 years resulted from traffic accidents at locations less than 500 m distance from their homes (IATSS, 2007).

Positive Outcomes of Traffic Calming: Reduced Severity and Frequency of Accidents

Traffic calming can significantly reduce accident risk, specifically for pedestrians and cyclists. In North America, in areas where 20 miles per hour (mph) zones are established, the number of collisions has decreased and the number of injured children, either walking or bicycling, has been reduced by 67% (Victoria Transport Policy Institute, 2008). Traffic accidents occur as a result of unsafe acts by agents of traffic behaviors in the form of pedestrians, cyclists, and/or drivers. In other words, people, coupled with a defective, undesirable traffic environment, cause accidents. Traffic calming is a method to control traffic so that its negative impacts on residents and pedestrians are minimized. Reducing traffic speeds and volumes can reduce the severity of vehicle crashes, particularly those involving pedestrians and bicyclists (Zein et al., 1997).

The concept of traffic calming encompasses efforts to design new neighborhoods' street network in so that traffic volume and speed are minimized (Rahman and Kubota, 2016).

Traffic calming can effectively reduce vehicle speeds and thereby ensure safety for pedestrians and cyclists. The severity of pedestrian injuries caused by vehicle collisions increases with the square of the vehicle speed. Lower vehicle speeds reduce the likelihood of crashes and the degree of damage that may result (Leaf and Preusser, 1998). Therefore, traffic calming can significantly reduce the crash risk, particularly for pedestrians and cyclists.

Considering potential traffic diversion effects

Traffic calming of an intersection, road, or area can have the effect (intended or unintended) of diverting traffic toward other roads or sectors of a city, which bears the risk of simply displacing the problems being addressed. Area-wide traffic calming strategies, in particular, often explicitly aim to redirect a portion of traffic on local streets toward the arterial network (Gagnon and Bellefleur, 2011).

Factors influencing pedestrian-friendly roadway design and speed management

Roadway design speed, not posted speed, is the most influential factor in determining roadway operating speed. In general, the following factors encourage slow speeds and hence serve as positive influences on the overall pedestrian environment (Jaskiewicz, 2000):

• Narrow lane widths, i.e., 3.0 to 3.4 meters lanes as opposed to 3.7 to 4.3 meters lanes.
• Narrow overall paved widths. In general, two-lane roadways are more pedestrian-friendly than six-lane roadways, though careful attention to design can largely offset this inherent disadvantage of high-volume thoroughfares. The effect of a bicycle lane is largely negligible, since it adds to overall paved width but at the same time provides additional separation (buffer) between pedestrians and automobiles.
• Broken sight lines. The longer the unimpeded view down the roadway, the faster the motorist will feel comfortable driving. Such a view can be broken up through the placement of in-street traffic calming devices such as roundabouts and splitter islands, or by designing the roadway to meander slightly back and forth along its length.
• Sharp turns. Smoothly curving roadways and large corner radii allow vehicles to navigate comfortably at high speeds, while jagged, “kinked” roadways and small corner radii require motorists to drive slowly to perform turning maneuvers, giving them more time to see and react to pedestrians and bicyclists.
• On-street parking. In addition to contributing to an overall sense of enclosure and narrowness, on-street parallel or diagonal parking increases motorists’ overall levels of alertness, requiring them to be constantly aware of the surrounding parked vehicles. This increased wariness improves the chances that motorists will notice pedestrians who attempt to cross the street.
• Treatment at pedestrian crossings. Special treatment at pedestrian crossings, such as bulb-outs and textured paving, can encourage motorists to drive with caution by increasing their awareness that pedestrians might be present. Raised crosswalks and speed bumps are often not desirable because they frustrate and anger motorists and hence increase the likelihood that they will drive unintelligently.
• Others like vehicle restrictions, warning signs, gateways, speed tables, raised crosswalks, median islands, channelization islands, rumble strips, mini-circles, roundabouts, radar clocked traffic speeds displayed to drivers, Radar speed camera and its sign, horizontal shifts (Pérez-Acebo, 2016).

Conclusion

Traffic calming measures are implemented to promote greener and more sustainable urban environments. Such as Rahman et al. (2005) justified for Japan, the traffic calming measures reduce vehicle speed and volume, reduce accident frequency and severity, protect neighborhood areas from the unwanted through traffic, ensure road safety for all users, especially pedestrians and cyclists, and reduce noise and air pollution.

References

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