Semi Trucks - Tractor Trailers and Large Delivery Trucks
Be Safe In City Traffic Around Cyclists, Pedestrians, and Motorcyclists
For pedestrians, bikes, small cars, scooters, mopeds, electric bikes, even small car drivers: being near a large truck in traffic on city streets is an everyday dangerous type of situation.
Large semi-trucks, dump trucks, and commercial vehicles present hidden dangers especially in city traffic to the most vulnerable roadway users: pedestrians, bikes and motorcycles. The problem is well known to traffic safety researchers; large trucks have large blind spots and the driver may not be able to see a pedestrian or bike in common city traffic situations. Additionally, large trucks are especially dangerous because of what is called an underride crash. Underride crashes are extremely dangerous not only for pedestrians, bicycles, motorcycles, but also occupants of passenger cars and trucks.
In an underride crash, a passenger vehicle goes partially or wholly under a truck or trailer, increasing the likelihood of death or serious injury to the passenger vehicle occupants. A 1997 Institute study of fatal crashes between large trucks and passenger vehicles estimated that underride occurred in half of these crashes. Of the underride crashes, 57 percent involved the front of the truck, 22 percent involved the rear, and 20 percent the side. [...]
There is no requirement for front or side underride guards in the United States. European Union regulations have required front underride guards on large trucks since 2003. Side underride guards, which are primarily intended to protect pedestrians and bicyclists, have been required in the EU since 1989. A 2012 Institute study found that in the US strong side underride guards could reduce injury risk in around three-fourths of cases where a passenger vehicle occupant sustained a serious injury from an impact with the side of a large truck. 
Pictured: car-truck rear underride crash
Despite new regulations in the USA, rear underride crash fatalities have not decreased since requirements for a rear crash guard were put in place in 1998. Some fault that the specifications of the rear guard are both inadequate in terms of the speed of the average rear collision and also that the height of the rear crash guard is actually too high to be effective.
In 2010, reviewing crash data on large truck verses car fatalities, researchers found no improvements since before the 1998 rear guard requirement. Still others insist, backed up by this data analysis, that rear crash guards are not sufficient as many deadly collisions occur with the sides of the semi-truck tractor trailer.
The total number of passenger vehicle fatalities when rear-ending a tractor-trailer has not decreased over the years in terms of total number of fatalities, percentage of fatalities in rear-end impacts relative to other passenger vehicle fatalities involved in tractor-trailer accidents, or in number of fatal crashes per 1,000 total crashes. 
As a rough estimate, the researchers noted that there would be 261 rear-end underride car-into-truck fatal collisions per year, and 195 side underrides per vear. [...] The report notes not only the large quantity and percentage (almost half) that are side and side-angular crashes. and also notes the majority (65 out of 87) were in the 30-to-50 mph range. 
Bicycle riders, pedestrians, and motorcycles are all especially vulnerable to the side impacts and many safety advocates call for the side guards to be a requirement on large semi-trucks in the USA, as they have been in Europe for decades. Still, some large trucks such as delivery trucks and dump trucks do not fall into the category of vehicle where even the rear guards are required in the USA, and as seen in the picture below, the danger of these vehicles is obvious.
Pictured: no rear guard required on a large dump truck in USA
Yet, there are many traffic safety researchers who are working on safety improvements. Things such as improved rear guards have been designed and crash tested in Brazil. In Europe, safety researchers have worked on better mirror systems, sensors to alert a driver to pedestrians or bikes in their blind spots, and even rethinking intersections to help all drivers have better views of the most likely places where people are hidden in their blind spots.
In the USA bicycle safety advocates call for these side guards to be made a requirement on all commercial trucks. The safety improvement would affect safety for cars, pedestrians, motorcycles and bicyclists. Safety advocates also call for the "tripod mirror" to be installed on all large trucks which will help the driver with improved visibility into the well-known and documented blind spots. These safety improvements can and will save lives and are not such giant structural changes that they would be inordinately expensive. As shown, these devices could work with any trailer or cab model, as well as be incorporated into new vehicle designs.
Pictured: Truck Side Guards
Underride crashes are definitely a point where many lives can be saved.
Trucks have large blind spots.
2. The Effectiveness of Underride Guards for Heavy Trailers