Update model_documentation.md

project_11_path_planning/model_documentation.md

@@ -24,3 +24,14 @@ Here's a bullet list of rubric points along with an explanation of how constrain
 
     A [reference velocity variable](https://github.com/ndrplz/self-driving-car/blob/7b0d9e057931667a04422649fee6d017b3ef7475/project_11_path_planning/src/main.cpp#L74) is used to keep track of current speed of the vehicle. Also, [another constant variable](https://github.com/ndrplz/self-driving-car/blob/7b0d9e057931667a04422649fee6d017b3ef7475/project_11_path_planning/src/utils.h#L13) is used to make sure the car never exeed the maximum speed of 50 mph.
 
+- **Max acceleration and jerk are not exceeded.**
+
+    The rubric sets as hard constraint the fact that car does not exceed a total acceleration of 10 m/s^2 and a jerk of 10 m/s^3. This is obtained by setting the initial speed of vehicle to zero, and [gradually accelerating](https://github.com/ndrplz/self-driving-car/blob/7b0d9e057931667a04422649fee6d017b3ef7475/project_11_path_planning/src/main.cpp#L181-L182) until the vehicle has reached the maximum speed allowed (either by the speed limit or by the current road situation).
+
+- **Car does not have collisions.**
+    Under the reasonable assumption that other cars drive reasonably well, the main risk to hit another car is *rear-ending*. This is avoided using [sensor fusion data to make sure that no other car is dangerously close](https://github.com/ndrplz/self-driving-car/blob/7b0d9e057931667a04422649fee6d017b3ef7475/project_11_path_planning/src/main.cpp#L133-L134) in our same lane. If this is the case, the car [gracefully decelerates](https://github.com/ndrplz/self-driving-car/blob/7b0d9e057931667a04422649fee6d017b3ef7475/project_11_path_planning/src/main.cpp#L179-L180) until the situation gets safer.
+
+    Another possibly dangerous situation is the one of *lane changing*. This will be examined in the next point.
+
+- **The car stays in its lane, except for the time between changing lanes.**
+- **The car is able to change lanes**