/// <summary>
        /// Remove a road user from the intersection.
        /// </summary>
        /// <param name="roadUser">The road user to remove.</param>
        public void RemoveRoadUser(RoadUser roadUser)
        {
            if (roadUser == null)
            {
                throw new ArgumentNullException("roadUser");
            }

            roadUsers.Remove(roadUser);
        }
        /// <summary>
        /// Add a road user to the intersection so that it can be painted on the intersection.
        /// </summary>
        /// <param name="roadUser">The road user to add.</param>
        public void AddRoadUser(RoadUser roadUser)
        {
            if (roadUser == null)
            {
                throw new ArgumentNullException("roadUser");
            }

            roadUsers.Add(roadUser);
        }