###### Contents  
* 1 Introduction
* 2.1 The impact  
Highway crashes are said to be a consequence of multiple factors, which are usually grouped in relation to the infrastructure (highway condition), the vehicle and the driver (human condition) [2; 10; 11; 12; 13; 14; 15]. However, in urban areas, but also in rural areas, one of the main problems in terms of road safety remains the excessive speed and speeding drivers [16; 17; 18; 19; 20; 21]. Moreover, with higher speeds, there is higher probability of pedestrian death, and it is not proportional, as shown in Table 1[22; 23]. Consequently, aiming to improve the road safety in urban areas, traffic calming measures (TCM) are being introduced. They can be defined as the combination of mainly physical measures that reduce the negative effect of motor vehicles use, alter driver behavior and improve conditions for non-motorized streets users [24]. Moreover, speed reduction helps protect other vulnerable users like cyclists [25; 26; 27]. Additionally, it must be highlighted that the special protection of vulnerable road users (motorcyclist, cyclist, mopeds and pedestrians) became a policy orientation of the European Commission [28]. Traffic calming schemes incorporate a wide range of measures intended to reduce speed and enhance the environment [20], although the effectiveness of them varies depending on the measures employed. Traffic calming measures are accurately defined and described in Ewing [29] and can be grouped into four categories:  
* Vertical deflection: speed hump, speed bump, speed cushion, rumble strip, raised crosswalk, raised intersection, road lump and table. * Horizontal deflection: curb-extension, chicane, gateway, raised median island, traffic circle
* Physical obstruction: semi and diagonal diverter; right-in and right-out island, raised median through intersections, street closure
* Signs and pavement markings. In previous studies speed was mostly investigated with regard to its reduction as a consequence of various measures' influence both in field experiments [30; 31; 32] or driver simulation studies focusing on chosen infrastructural impacts on drivers' behavior [33] and on the reduction of the number of accidents and injuries. The effectiveness of TCMs depends also on their type. Many researches proved that the most effective measures in speed and fatalities reduction are vertical deflections [34; 35], becoming the most employed ones [36; 37]. [PERSON] et al. [38] showed 60% decrease of fatal and injury accidents and 82% decrease of killed people on roads with vertical deflection in Lithuania. In terms of the percentage accident reduction, engineering schemes incorporating vertical deflections offer the largest benefits, becoming at least twice safer than sites where cameras were used to control speeds [39; 40; 41]. Additionally, [PERSON] et al. [42] indicated that the installation of speed humps is one of the TCMs with a benefit-cost ratio over 1 in all the scenarios, underlining its effectiveness. Apart from the type of the TCM, the shape characteristics of speed bumps and humps are important and influence drivers' behavior and driving comfort differently [43; 44; 45; 46]. [PERSON] et al. [47] conducted an experiment to determine the optimal design of speed bumps for reducing the velocity of vehicles without endangering road safety. With regard to the environment, the most important point seems to be fuel consumption car emissions as a result of driving style. Driving pattern in urban areas is characterized by a lower average speed and higher number of stops, implying both fuel consumption and pollutant emissions many times higher per vehicle-km. [PERSON] et al. [48] pointed that emission estimates should incorporate the acceleration instead of mean speed of vehicle and the effect of acceleration is higher at lower speed than at higher speeds. Due to costs, it is very common that traffic calming measures operate separately instead of adopting systematic solutions. Hence, their effectiveness, especially the most commonly used TCMs,