This brief analyzes the impacts of electric medium- and heavy-duty vehicles (e.g., trucks and buses) on hourly electric demand by state. We find that by 2030, these vehicles will add about 1,000 megawatts (MW) to peak load in Texas, about 500 MW to peak load in California, and 200-500 MW of peak load in 14 other states. These new loads should be factored into electric system planning including generation, transmission, and distribution. Often these loads will be on specific distribution circuits and will sometimes require new or expanded substations. Since new and expanded substations can take five years or more to propose, design, and build, plans need to be made today for loads expected by 2030.