code:
@ OnGameModeInit: SetTimer("Speed",250,1);
public Speed()
{
for(new i = 0; i <= USERCOUNT; i++)
    {
        if(IsPlayerConnected(i))
	{
	new Float:x, Float:y, Float:z, distance,result,resultx[256];
    x=PlayerInfo[i][PosX];
	y=PlayerInfo[i][PosY];
	z=PlayerInfo[i][PosZ];
	distance=GetDistance(i, x, y, z);
	result=distance*6;
 format(resultx,256,"%dkm/h",result);
	GameTextForPlayerBottom(i,resultx);
	
	new Float:x2,Float:y2,Float:z2;
	GetPlayerPos(i,x2,y2,z2);
	PlayerInfo[i][PosX]=x2;
	PlayerInfo[i][PosY]=y2;
	PlayerInfo[i][PosZ]=z2;
	}
	}
}
but function is not working well, it needs improvements.
sorry for my english.