[Vince]

GetVehicleVelocity just doesn't work like that. You need to parse them together to get a usable result (speed).
Use this function to determine the speed of a vehicle:

pawn Код:

stock GetPlayerSpeed(playerid, bool:kmh = true)
{
    new
        Float:xx,
        Float:yy,
        Float:zz,
        Float:pSpeed;

    if(IsPlayerInAnyVehicle(playerid))
    {
        GetVehicleVelocity(GetPlayerVehicleID(playerid),xx,yy,zz);
    }
    else
    {
        GetPlayerVelocity(playerid,xx,yy,zz);
    }

    pSpeed  = floatsqroot((xx * xx) + (yy * yy) + (zz * zz));
    return kmh ? floatround((pSpeed * 195.12)) : floatround((pSpeed * 121.9));
}

Use:
For km/h: new speed = GetPlayerSpeed(playerid);
for mph: new speed = GetPlayerSpeed(playerid, false);