Impact on truckers, though it is barely mentioned in the congestion-charge literature, is probably more important than impact on the poor -- because (1) there probably are more peak-hour truckers than there are low-income drivers; (2) trucks will cause up to 80% of the projected growth in some corridors; (3) the truckers are much more organized than low-income drivers, and their voice is more likely to be heard in the state legislature; and (4) truckers' role in creating and supporting jobs, and supplying goods and services, is far larger and more consequential to the poor (to say nothing of the non-poor) in general than is commuting by a small number of poor individuals. Modern, just-in-time manufacturing already relies heavily on free access by truck. It will probably rely even more so in the future.
Trucks are not likely to be much affected by start-up HOT lanes unless, as seems improbable now, they are permitted to buy onto them. To the extent that start-up, add-a-lane HOT lanes speed up general lanes, they would come out a bit ahead. If and when the charge system approaches full scale, and every available lane is a HOT lane, wholesale exclusion of trucks will no longer make sense. They will need available access to at least some of the lanes at peak hours, and they should pay for it, just like everyone else. How much? I don't have a study of it, but three times as much per mile might be a plausible guess, since trucks are bigger and cause much more congestion, both recurrent and non-recurrent, than cars. They also cost more to own and operate, maybe $100 an hour with driver, and their drivers are not strangers to deadlines. If they could pay, say, a $15 congestion charge and thereby save 15 minutes, they would save $25 worth of operating time and come out $10 ahead, maybe more when the deadline is really tight. If this were a typical situation (as it probably would be), and the whole of the bargain, truckers should be demanding congestion charges now to get themselves into the fast lane.
However, it may not be the whole of the bargain. Any time the talk turns to user fees, it could turn also to other use impacts which truckers would rather not have on the agenda, such as charges for road wear and for nonrecurrent congestion imposed by accidents. Many think trucks are disproportionately responsible for both of these and are not paying their full share of the costs (Small, et al., 1989). The same could be said of a modern, particulates-dominated estimate of smog costs. Small and Kazimi, for example, reckon smog costs per mile at 3 cents a mile for cars, 53 cents per mile for heavy diesel trucks (1995, p. 25. But see Appendices One and Fourteen of the longer version for reasons to believe PM10 costs from trucks may be exaggerated). To the extent that these are so, truckers could lose, as well as gain, from a comprehensive application of the pay-for-what-you-use principle. A closer study of the congestion issues, including nonrecurrent, could help sort some of these questions out. Pending such studies, it seems more likely than not that full-scale congestion charges, by themselves, would be a boon to truckers. SCAG is currently contracting for feasibility studies for truck-only toll lanes on several of the truck-impacted highways.