toribio

public OnPlayerUpdate(playerid)
{
    if(!IsPlayerNPC(playerid))
    {
        new
            keys, udlr;

        GetPlayerKeys(playerid, keys, udlr, udlr);
        if((GetPlayerState(playerid) == PLAYER_STATE_DRIVER) && ((keys & 4) || (keys & 1)))
        {
            new
                Float:x, Float:y, Float:z,
                vehicleid = GetPlayerVehicleID(playerid);

            GetVehicleVelocity(vehicleid, x, y, z);
            if(keys & 4)
            {
                SetVehicleVelocity(vehicleid, x + (x / 4), y + (y / 4), z + (z / 4));
            }
            else if(keys & 1)
            {
                SetVehicleVelocity(vehicleid, x - (x / 18.0), y - (y / 18.0), z - (z / 18.0));
            }
        }
    }
    return 1;
}