From the link you gave above:

Cars and tornadoes can prove a dangerous mix even for the world's most experienced storm chasers. Driving at high speeds though heavy rain, large hail, and high winds is hazardous. If one is lucky enough to chase down a tornado, even the most experienced chasers can find themselves in a serious life-threatening situation when unexpected events occur.

The exact circumstances of the deaths of Tim Samaras and his team are not clear, but the El Reno tornado was an extremely dangerous one to chase. It's particularly dangerous when a tornado is wrapped in rain, making it hard to see, or if a chaser is operating in a heavily populated area, where roads may suddenly become congested.

El Reno tornado was wrapped in rain and difficult to see as it headed west towards Oklahoma City, and suddenly made a jog to the southeast as a Weather Channel team led by Mike Bettes was attempting to get in front of the storm, and the tornado lifted their vehicle off the ground, rolled it multiple times, and hurled it 200 yards into a nearby field.

Austin Anderson was driving the Tornado Hunt vehicle, and suffered several broken bones and was hospitalized. Although Austin will have to undergo surgery in the next few days, doctors say he is expected to make a full recovery.

StormChasingVideo.com storm chaser Brandon Sullivan and his chase partner Brett Wright got caught in the tornado northwest of Union City, OK and slammed with debris as the tornado hit a barn that exploded in front of them.

Meteorologist Emily Sutton and storm chaser Kevin Josefy of local Oklahoma City TV station KFOR also had a very close call with the El Reno tornado Friday afternoon. They got too close to the tornado, and were forced to floor the car in reverse to escape flying debris. With branches of trees crashing around them, Sutton began feeling debris hitting her back, and realized that the rear windshield of the car must have gotten destroyed. Both were uninjured.

Reed Timmer's armor-plated "Dominator" chase vehicle had its hood torn off by the tornado.

Wunderground member Levi32 was out storm chasing during the El Reno Tornado, and got stuck in traffic on Highway 4 and couldn't move. "We looked up above the car and saw the wall cloud over top of us, with very quick rotation and rising scud indicating the updraft. We were definitely too close."