Wheelchair accessible van

A wheelchair-accessible van is a vehicle that has been modified by increasing the interior size of the vehicle and equipping it with a means of wheelchair entry, such as a wheelchair ramp or powered lift.
Modifications.
The general steps manufacturers undergo to convert a van differ greatly from one manufacturer to another.
Modifications fall into two categories, the first is where the individual in a wheelchair is the driver and the second is where the individual in a wheelchair is a passenger.
Conversions generally involve the following:
Typical converted vehicles come with a 3 year 36,000-mile warranty. One modern conversion (FR Conversions side entry Crosswind) comes with a 10 year 100,000-mile warranty.
Passenger conversions on buses or a full size van involve the following:
Entry configurations.
There are two types of entry configurations: side-entry and rear-entry. The entry location impacts wheelchair seating positions, parking options, the ability to accommodate other passengers, and storage availability.
Side entry.
Advantages of a side-entry configuration include: ability to drive from a wheelchair or sit in the front passenger position in a wheelchair or driver position; enter and exit curbside away from traffic; and more storage space. Disadvantages of this style are that it requires a handicap parking space or extra room for ramp deployment and that some driveways are not wide enough to accommodate the vehicle. About 65% of personal use wheelchair-accessible vehicles employ a side-entry configuration. Side entry vehicles can accommodate 5 passengers at most and typically are typically limited by total maximum load because of the extra weight of the conversion and often cannot seat more than 2-3 passengers based on total weight.
Rear entry.
A rear-entry configuration can be used for attended applications in which the wheelchair occupant is not driving the vehicle but rather riding as a passenger. Rear entry vehicles are simpler, much less costly, require virtually no extra maintenance. Ride and drive quality are very similar to an unconverted vehicle. They will fit into any garage. Other advantages of a rear-entry vehicle is that, with the exception of parallel parking, no extra room is required for a ramp, and the side passenger doors aren’t blocked. In addition, mid-passenger seats can be mounted next to the wheelchair position. Other advantages include more ground clearance and more room for long wheelchairs and/or leg rests. One manufacturer (FR Conversions) makes a 48" wide RE ramp. The widest in the industry which can handle virtually any wheelchair. 
Rear entry vehicles are often converted from good used vehicles into a "Used / New" configuration which is much more affordable and places a wheelchair accessible vehicle within reach of many in need who otherwise could not afford one. It is a great 'starter" vehicle for consumers who are unsure of which configuration would work best and is a good entry point from a wheelchair carrier to one where transferring is no longer necessary. 
Limitations of the rear-entry style are the requirement to enter and exit from a traffic area although no special parking space is required. The inability to drive from the wheelchair and/or have the wheelchair in the front passenger position and less storage space are disadvantages. Rear entry vehicles are available in two configurations. Long cut and short or taxi cut. The long cut handles two wheelchairs the short cut one. Seating can be arranged so rear-entry vehicles can seat up to 6-8 passengers.
Types of access.
Ramp.
Ramp based modifications are most commonly performed on minivans. In order to provide access for the wheelchair user, the floor on side-entry vehicles is lowered . In rear-entry configuration, the floor is not lowered but rather removed, and a composite or steel tub is inserted.
Ramps come in two styles—fold-up or in-floor—and two operating modes—manual or motorized. Fold-up ramps fold in half and stow upright next to the side passenger door in a side-entry configuration or inside the rear access doors in a rear-entry configuration. Fold-up ramps present a lower ramp angle than in-floor ramps; however, in side-entry configurations, they are in the way of the passenger entrance when stowed. In-floor ramps slide into a pocket underneath the vehicle's floor and are only available for side-entry configurations. 
Folding ramps are available in manual or motorized versions for both entry configurations. Older style applications may also have a “kneeling feature” that reduces the angle of the ramp by compressing the suspension of the van on the ramp side, newer ones using complex geometry eliminate the need for kneeling to meet ADA standards although they may employ a retracting system as an option, that eliminates the stress of compressing the suspension. 
Some other advantages of the fold-out ramp for the side entry vehicle are that an unaccompanied wheelchair driver can "Self Rescue" in the event of a system failure and not become trapped in the vehicle; ramp deployment onto a sidewalk or over a curb is sometimes only possible with a fold-out ramp because it will deploy out and over the curb; in very snowy climates the ramp remains inside the vehicle, away from the weather. A secondary disadvantage of the side entry fold-out ramp is that they rattle inside the vehicle. Modern, solenoid controlled ramps with actuators on both sides of the ramp are self tightening and eliminate the issue.
The primary advantages of the in-floor ramp configuration are that ambulatory passengers have access to the vehicle from the curb side of the vehicle; and the ramp is stowed under the floor. The possible disadvantages are that the ramp is not able to overcome or deploy onto higher curbs, snow and ice may be retained in the ramp"tray"; not all models are ADA compliant because of the ramp's side edge height; self-rescue is not possible. 
In addition, portable ramps are available for use with many vehicles and typically do not require any vehicle modification. Portable wheelchair ramps cost much less both to purchase and to maintain. Since they are not attached to the vehicle, they can also be used for handicapped access for other applications.
Minivans that are most frequently converted:
Other much less common conversions include a Ford (Braun) and a Honda (VMI) SUVs and a Ford Transit Connect(Mobility Works).
Full Size Vans
Some manufacturers also provide wheelchair accessible versions of their out going vehicles:
Platform lifts.
Full size vans require lifts in the form of a platform that can be raised and lowered from inside the vehicle down to the ground outside.
There are many types of lifts available on the market. Mono-arm lifts, double-arm lifts and under vehicle (UVL) lifts. Double-arm and underbody lifts are best-able for bigger vehicles such as minibuses or buses used for public transport. They have a bigger platform and higher load capacity so they are suitable even for heavy electric wheelchairs with a heavy occupant (more than 600lbs in all). A mono-arm Lift is preferable for private transport because it can fit smaller vehicles. A mono-arm lift is lighter and smaller than the other ones and it ensures a clear view when it is installed in the back of the car. Moreover, mono-arm lifts are preferable for the side-door installation because they are thinner than a double-arm.
Other types.
Crane type lifts are combined with seats that turn and lower to the ground as a means of providing wheelchair access to some types of vehicles.
Some companies offer the option of a "transfer seat", in which the front driver's or passenger's seat moves on a track back to the wheelchair's position allowing the wheelchair user to transfer into the OEM front seat and then move the seat back into its original position. The conversion is very simple and does not carry the complicated engineering and electronics typically found in a side-entry conversion. As a result, they are very well suited for commercial and heavy-cycle applications (i.e.-taxi, non-emergency ambulance, paratransit, assisted living, and dial-a-ride) and geographic areas prone to vehicle corrosion from salt and chloride usage on highways in winter seasons.