When planting pollinator habitat adjacent to a road, how big of a concern is mortality by vehicle traffic?

While vehicle traffic is a contributor to adult monarch mortality, more research is needed on this issue to know the full extent. However, given the extreme loss of habitat that monarchs and others have faced, we feel confident that the benefits of planting pollinator habitat along roadsides outweigh the cost. You can read more on roadside threats and opportunities for pollinators in this literature review  for the Federal Highways Administration conducted by the Xerces Society.