Here is some driving advice, taken from the Arkansas Driver License Test Study Guide, which addresses the challenges of safely merging with traffic. You may want to pass this along to your drivers as a friendly reminder. 

When you merge with traffic, try to enter at the same speed that traffic is moving. High-speed roadways generally have ramps to give you time to build up speed. Use the ramp to reach the speed of the other vehicles before you pull onto the road. Do not drive to the end of the ramp and stop. This will not leave you enough room to get up to the speed of traffic. Also, drivers behind you will not expect you to stop. If they are watching traffic on the main road, you may be hit from the rear. If you have to wait for space to enter the roadway, slow down on the ramp so you have some room to speed up before you have to merge.