[Logic_]

Not trying to offend you, but you're offering to teach scripting where you've none to less scripting and actual knowledge of SA-MP. Some stuff that I'd suggest you is, that you read the SA-MP wiki, it has almost everything you need.

Use 1000 ms (1 second) timer, and call it under OnGameModeInit, kill it under OnGameModeExit. Use foreach or player-pool size loop instead of MAX_PLAYERS loop, I'd recommend foreach though, but it's totally up to you that which one you choose to use.

EDIT: Example given below:

PHP код:

// Along with other defines
#define METRES_TO_FEET(%0) \
    ((%0) / 0.3047999995367040007042099189296)
// Under OnGameModeInit
SetTimer("updateVehicleTD", 1000, true);
// Somewhere in the script
forward    updateVehicleTD();
public    updateVehicleTD()
{
    new string[50], Float: vehX, Float: vehY, Float: vehZ, vehHealth;
    foreach(new i : Player)
    {
        if(IsPlayerInAnyVehicle(i))
        {
            format(string, sizeof string, "~b~KM/H: ~w~%d", GetKMHSpeed(i));
            PlayerTextDrawSetString(i, vehKMH[i], string);
            GetVehicleHealth(GetPlayerVehicleID(playerid), vHealth);
            format(string, sizeof string, "~b~Health: ~w~%0.0f", vHealth);
            PlayerTextDrawSetString(i, vehHealth[i], string);
            GetVehiclePos(GetPlayerVehicleID(playerid), vehX, vehY, vehZ);
            format(string, sizeof string, "~b~Altitude: ~w~%d M", floatround(METRES_TO_FEET(z)));
            PlayerTextDrawSetString(i, vehAlt[i], string);
        }
    }
    return 1;
}