How many drivers to hire per van: the relief factor for time off, call-outs, and turnover

Start from driver shifts, not vans

The number of drivers you need depends on how many driver shifts you run, and then on how often the people who fill them are away. Vans are only the starting point. A wheelchair van on the road from 5:00 AM to 7:30 PM needs two shifts a day, and a van that also runs Saturday dialysis needs a sixth day covered.

The fleet size calculator handles the first step. It turns trip volume into vehicles and then into drivers per day, by multiplying the vehicles on the road by the service day divided by the shift length. In its preloaded example, 7 vehicles on the road over an 11-hour service day with 8-hour shifts need 10 drivers a day. The driver shifts guide shows how to place those shifts against your demand curve.

Ten drivers a day is not a roster of ten. Every one of them takes vacation, gets sick, goes to training, and eventually quits. The relief factor is how you account for that.

What the relief factor measures

The relief factor is the number of people it takes to keep one seat filled all year. It comes from one division:

Relief factor = days the seat must be filled in a year ÷ days one driver actually works in a year

A seat filled five days a week needs 260 days of coverage. If a full-time driver scheduled for those 260 days is away 22 of them, they work 238, and the relief factor is 260 ÷ 238, about 1.09. Multiply your weekly driver shifts, converted to full-time positions, by that factor and you have the roster before turnover.

Transit agencies have managed the same problem for decades with what they call the extraboard. A 2007 report for the Florida Department of Transportation, by the National Center for Transit Research, quotes the American Public Transportation Association’s definition: the roster of operators who, by seniority or choice, have no regularly assigned run. The report notes that operator absence usually dominates the need for an extraboard, ahead of unassigned work and non-driving assignments such as training. In its survey, full-time extraboard operators averaged 19.6% of all operators at large systems, 12.1% at medium systems, and 5.9% at systems with fewer than 50 buses. Those are bus fleets, so treat the figures as a range to compare against, not a target.

The days each driver is away

Build the denominator from your own policy and last year’s records. The categories below cover most of it.

• Vacation. Whatever your policy grants. Ten days a year is common for full-time staff, but use your own number.
• Holidays you still run. A paid holiday when the office closes costs nothing to cover. A holiday when dialysis runs still go out is an absence that someone has to fill.
• Sick leave. State law sets the floor. California accrues at least one hour per 30 worked and lets employers cap yearly use at 40 hours or five days, usable from the 90th day of work. New York also accrues one hour per 30, with up to 40 paid hours a year at employers with 5 to 99 employees and 56 at 100 or more. Washington accrues one hour per 40 worked.
• Other unplanned absence. Bureau of Labor Statistics data for 2025 put the lost worktime rate for transportation and material moving occupations at 1.8%, meaning hours absent as a share of hours usually worked. It counts illness, family obligations, and civic duty, and leaves out vacation and holidays. On a 260-day year, 1.8% is about 4.7 days, which lines up with the five sick days most state laws produce.
• Training days. Refresher courses, CPR renewals, and broker-required training take drivers off the road. Count the days you schedule.
• Long leaves. Once your headcount reaches 50 on every working day of 20 calendar workweeks, eligible drivers can take up to 12 workweeks of FMLA leave a year. The Florida report calls the seat a long leave leaves open a “hold-down,” because it has to be held until the operator returns.

Turnover: the seat that sits empty

Quits add a second kind of gap: the days between a driver’s last shift and the first solo shift of the replacement. Notice periods, screening, and the new driver’s training and ride-alongs all fall in that window, and the hiring guide shows how long each step takes.

National data give a sense of scale. BLS reports an annual average quits rate of 2.2% a month for transportation, warehousing, and utilities in 2025. Over twelve months that is roughly 26% of the industry’s average workforce quitting, before layoffs and firings. Your own rate may be far from that, so use your records. To see what each departure costs in dollars, try the driver turnover cost calculator, and the driver retention guide covers ways to lower the number.

To add turnover to the roster, multiply the departures you expect in a year by the working days each seat sits empty, then divide by the days one driver works. The result is the extra share of a driver you carry for vacancies.

Worked example: from 7 vans to a roster

This example uses the 7 vehicles on the road from the fleet calculator’s preloaded example and a made-up leave policy. Replace every figure with your own.

1. Count weekly driver shifts. Ten driver shifts each weekday and four on Saturday for dialysis make 54 shifts a week.
2. Convert to full-time positions. At five shifts per driver, 54 ÷ 5 = 10.8 positions.
3. Count days away per driver. 10 vacation days, 3 holidays on which service runs, 5 sick days, 2 training days, and 2 other days add up to 22. A driver works 260 − 22 = 238 days.
4. Apply the relief factor. 260 ÷ 238 ≈ 1.09, and 10.8 × 1.09 ≈ 11.8 positions.
5. Add turnover. If 3 drivers leave in a year and each seat sits empty for 15 working days, that is 45 driver days, or 45 ÷ 238 ≈ 0.19 positions.
6. Total. 11.8 + 0.19 ≈ 12.0 full-time positions, against 10.8 with nobody ever absent.

The same numbers tell you how many open shifts to expect. Absences leave 54 × 22 ÷ 260 ≈ 4.6 shifts open in an average week, and vacancies add about 45 ÷ 52 ≈ 0.9 more. Plan for five or six open shifts in a typical week, and more in the weeks when vacations cluster.

Run the count separately for each kind of driver you cannot swap. A driver trained only for sedans cannot cover a wheelchair run, and if your stretcher runs use two-person crews, both seats need relief.

A part-time bench or overtime

Five open shifts a week can be covered three ways, and they cost different amounts:

Overtime looks easy because the drivers are already on staff. Federal overtime is time and a half on the regular rate once a week passes 40 hours (29 CFR 778.107), so each 8-hour shift covered that way costs 12 hours of pay. The Florida transit report adds a cost the payroll does not show. A 1984 survey of California agencies it reviewed found that long, irregular hours strain operators and lead to more time off, and that morale can suffer when understaffing calls operators in on their days off. The same survey noted that agencies leaning on overtime instead of an extraboard likely see regular operators take more unscheduled days off.

Overtime still has a place. A two- or three-van company with rare absences may not have enough open shifts to keep a part-timer interested, and the owner often covers. Keep every driver inside your fatigue rules and any hours limits that apply. The driver fatigue guide and the overtime guide cover both.

A bench works best when it is real. Give each part-timer a regular day, such as the Saturday dialysis run, so they keep the routes, riders, and vans fresh. Hold them to the same screening and training as full-time drivers. The driver requirements guide lists what brokers check.

Check the roster every quarter

A relief factor goes stale as policies, contracts, and people change. Once a quarter, compare it with what actually happened:

1. Count open shifts per week from the schedule, and note how each was covered: bench, overtime, or a trip handed back.
2. Total the days away by category and see which one grew.
3. Recount departures and the days each seat sat empty.
4. Recompute the factor and adjust hiring before summer and the December holidays, when vacations bunch up.

Cap how many drivers can be on vacation in the same week, so the bench is never asked to cover more than it can. The call-out guide covers the morning a driver phones in sick. The roster has a vehicle counterpart too: the spare ratio does for vans what the relief factor does for drivers.

Keeping the roster visible in HealthRide

HealthRide keeps a standing weekly pattern for each driver, turns it into the coming two weeks of shifts with one click, and lets you change a single day when someone is out or a substitute steps in. The dispatch board lists just the drivers working that day, and Ryder Go can plan your whole day in one click. Timecards from real clock-ins show who actually worked, which is the record you need when you recompute the relief factor each quarter.