not only directly by dint of vehicular safety performance per se, but also indirectly through the relatively low fuel costs that facilitate the use of such vehicles in north america; motor vehicle fatalities decline as fuel prices increase. the us nhtsa has issued relatively few regulations since the mid-1980s; most of the vehicle-based reduction in vehicle fatality rates in the us during the last third of the 20th century were gained by the initial nhtsa safety standards issued from 1968 to 1984 and subsequent voluntary changes in vehicle design and construction by vehicle manufacturers. issues for particular demographic groups pregnant women when pregnant, women should continue to use seatbelts and airbags properly. a university of michigan study found that "unrestrained or improperly restrained pregnant women are 5.7 times more likely to have an adverse fetal outcome than properly restrained pregnant women". if seatbelts are not long enough, extensions are available from the car manufacturer or an aftermarket supplier. infants and children children present significant challenges in engineering and producing safe vehicles, because most children are significantly smaller and lighter than most adults. additionally, children far from being just scaled down adults, still have an undeveloped skeletal system. this means that vehicle restraint systems such as airbags and seat belts, far from being effective, are hazardous if used to restrain young children. in recognition of this, many medical professionals and jurisdictions recommend or require that children under a particular age, height, and/or weight ride in a child seat and/or in the back seat, as applicable. within europe ece regulation r44 dictates that children below 150 cm must travel in a child restraint that is appropriate for their weight. each country have their own adaptions of this regulation. for instance, in the united kingdom, children must travel in a child restraint until they are 135 cm tall or reach 12 years of age, which ever comes soonest. as another example, in austria, the driver of passenger vehicles is responsible for people shorter than 150 cm and below 14 years to be seated in an adequate child safety seat. moreover, it is not allowed for children below the age of 3 to ride in a passenger vehicle without "security system" (which in practice means the vehicle is not equipped with any seat belts or technical systems like isofix), whereas children between 3 and 14 years have to ride in the back seat. sweden specify that a child or an adult shorter than 140 cm is legally forbidden to ride in a place with an active airbag in front of it. the majority of medical professionals and biomechanical engineers agree that children below the age of two years old are much safer if they travel in a rearward facing child restraint. child safety locks and driver-controlled power window lockout controls prevent children from opening doors and windows from inside the vehicle. infants left in cars very young children can perish from heat or cold if left unattended in a parked car, whether deliberately or through absent-mindedness. in 2004, the u.s. nhtsa estimated 25 fatalities per year among children left in hot cars. teenage drivers in the uk, a full driving licence can be had at age 17, and most areas in the united states will issue a full driver's license at the age of 16, and all within a range between 14 and 18. in addition to being relatively inexperienced, teen drivers are also cognitively immature, compared to adult drivers. this combination leads to a relatively high crash rate among this demographic. in some areas, new drivers' vehicles must bear a warning sign to alert other drivers that the vehicle is being driven by an inexperienced and learning driver, giving them opportunity to be more cautious and to encourage other drivers to give novices more leeway. in the u.s. new jersey has kyleigh's law citing that teen drivers must have a decal on their vehicle. some countries, such as australia, the united states, canada and new zealand, have graduated levels of driver's licence, with special rules. by 2010, all us states required a graduated driver's licence for drivers under age 18. in italy, the maximum speed and power of vehicles driven by new drivers is restricted. in romania, the maximum speed of vehicles driven by new drivers (less than one year in experience) is 20 km/h lower than the national standard (except villages, towns and cities). many u.s. states allow 18-year-olds to skip some requirements that younger drivers would face, which statistics show may be causing higher crash rates among new drivers. new jersey has the same requirements for new drivers up to the age of 21, which may obviate this problem. medical conditions according to a study published in 2017 in the mayo clinic proceedings, although most drivers with medical conditions were safe drivers, drivers with psychiatric conditions or substance abuse were particularly at higher risks of unsafe driving. the study also reported that drivers with neurological conditions were the majority of the entire study population (belgium) who were referred for a driving evaluation, but they were not the most unsafe drivers. elderly insurance statistics in the united states indicate a 30% increase in the number of elderly killed, comparing 1975 to 2000. several states require additional testing for elderly drivers. on a per-driver basis, the number of fatal and overall crashes decreases with age, with some exceptions for drivers over 75. the overall trend may be due to greater experience and avoiding driving in adverse conditions. however, on a per-miles-travelled basis, drivers younger than 25-30 and older than 65-70 have significantly higher crash rates. survivability of crashes decreases monotonically with the age of the victim. a common problem for the elderly is the question of when a medical condition or biological aging presents a serious enough problem that one should stop driving. in some cases, this means giving up some personal independence, but in urban areas often means relying more on public transportation. many transit systems offer discounted fares to seniors, and some local governments run "senior shuttles" specifically targeted at this demographic. vehicle programs while it is usually considered that the driver has the responsibility when collisions occur, vehicle can also contribute to collisions, up to 3% to 5% of crashes. two kinds of programs exist: new car assessment program for new cars, and vehicle inspections for other ones. ncap consumer information label for a vehicle with at least one ncap star rating a new car assessment program is a government or institutional car safety program tasked with evaluating new car designs for performance against various safety threats. two well known ncap are united states new car assessment program since 1978 and european new car assessment programme since 1997. legal vehicle inspections vehicle inspection is a procedure mandated by national or subnational governments in many countries, in which a vehicle is inspected to ensure that it conforms to regulations governing safety, emissions, or both. inspection can be required at various times, e.g., periodically or on the transfer of title to a vehicle. if required periodically, it might be termed periodic motor vehicle inspection, or mot test in the uk, or roadworthiness test in eu directives. typical intervals are every two years (in eu) and every year (in uk). when a vehicle passes inspection, often a sticker is placed on the vehicle's windshield or registration plate to simplify later controls, but in some countries (such as netherlands since 1994) this is no longer necessary. vehicles are tested at inspection stations when due for inspection. most us inspection decals/stickers display the month's number and the year. they are called testing centre in eu directives. vehicle inspection exists in the united states. in victoria, australia, safety features checked include the structure of the vehicle, the tires (depth of tread), the wheels, the engine, steering, suspension, brakes, and lights and seatbelts. other safety measures tires should be checked regularly. tire checking is important, because proper contact between tire and road is required for adequate vehicle control.