Below are health impacts of light rail systems.

Research shows that using light rail increases walking. Frank et al. (2004) report that obesity around Atlanta, as measured by body mass index (BMI), is associated positively with time spent in cars and negatively with mixed land-use (such as incorporating Light Rail transit) and with walking. There is also research which suggests that utilizing Light Rail transit increases physical activity even compared to riding the bus. Users of public transit who do not use trains, including light rail, walk an additional six minutes compared with non-users, whereas those who use trains including light rail walk an additional 4.5 minutes, for a total of 10.5 extra minutes per day. Additionally, MacDonald, et al. (2010) used data collected pre and post light rail development in Charlotte, North Carolina to determine that residents who commuted via light rail had 81% reduced odds of becoming obese.

Moreover, bicycle access to light rail transit can increase physical activity, as people will generally bicycle three to five miles to transit, as opposed the one‐half mile distance the average person is willing to walk. Research also shows that less time spent driving results in a reduced stress level, resulting in a higher quality of life.

Though there are significant potential public health benefits due to light rail, some studies have indicated the discrepancy between the enormous costs of building and operating light rail and its significant, but certainly smaller potential benefit to public health costs (estimated at $12.6 million savings over 9 years).

One electric light rail train produces about 62 percent less carbon monoxide and hydrocarbon emissions per mile than one automobile does. A report from the American Public Transit Association (APTA) presents evidence that each person riding light rail transit versus driving an automobile for one year reduces hydrocarbon emission by nine pounds, nitrogen oxide emissions by five pounds and carbon monoxide emissions by 62.5 pounds.

Some negative consequences are increases in noise level, loss of wetlands, adverse impacts to historic sites, gentrification, and risk of displacement. A 2011 study done by Human Impact Partners in Minnesota showed that light rail and RTD expansion in their communities had at least one if not all of these negative outcomes: higher rate of residential and business displacement, increase in housing values causing fewer vacancies and a decrease in affordable housing, and displacement of existing residents—especially low income residents. The study showed that there was a disproportionate impact on minorities and people with lower socio-economic status compared to European people and people with high socio-economic status. Moreover, the risk of displacement can also lead to negative health outcomes such as infectious disease, chronic disease, stress, and impeded child development due to lack of sense of belonging and association to a particular community.

Automobile injury hazards arise due to existing light rails. Coifman et al. (1997) concluded that drivers engage in undesirable behaviors or actions which are difficult for light rail operators to respond to due to insufficient warning time. Driver's actions such as disobedience to traffic rules and signs, as well as failure to perceive due to poor stimulus observability are factors of hazard causation. Additional factors include the misinterpretation of a light rail vehicle horn as another automobile's horn, and the driver's expectation of a normal intersection when in actuality the intersection includes a light rail crossing.

Pedestrians are also at risk of being injured by light rail vehicles, either by crossing rail tracks or ignoring traffic signs, especially where there is limited walkability to safely access the rail stop area. Currently, there is minimal literature available for pedestrian and automobile safety measures and traffic safety concerns (Brown et al., 2011). Further investigation and data collection is needed to accurately assess these risks.