Perhaps one technique to help people do this would be to draw signs that suggest two lanes merging rather than one lane ending and one continuing. So for examp

Perhaps one technique to help people do this would be to draw signs that suggest two lanes merging rather than one lane ending and one continuing. So for example if you have some flashing lights to mark the end of the lane, also put some flashing lights on the side of the road next to the other lane. That way people think "these lights are on both sides of the road, squeezing us down into one lane" rather than "these lights mark the end of that lane, while this one continues"