--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/python/traffic_engineering.py	Sat Apr 10 20:46:33 2010 -0400
@@ -0,0 +1,94 @@
+#! /usr/bin/env python
+''' Traffic Engineering Tools.'''
+
+from math import ceil
+
+__metaclass__ = type
+
+#########################
+# traffic signals
+#########################
+
+class Volume:
+    '''Class to represent volumes with varied vehicule types '''
+    def __init__(self, volume, types = ['pc'], proportions = [1], equivalents = [1], nLanes = 1):
+        '''mvtEquivalent is the equivalent if the movement is right of left turn'''
+
+        # check the sizes of the lists
+        if sum(proportions) == 1:
+            self.volume = volume
+            self.types = types
+            self.proportions = proportions
+            self.equivalents = equivalents
+            self.nLanes = nLanes
+        else:
+            pass
+
+    def getPCEVolume(self):
+        '''Returns the passenger-car equivalent for the input volume'''
+        v = 0
+        for p, e in zip(self.proportions, self.equivalents):
+            v += p*e
+        return v*self.volume
+
+class IntersectionMouvement:
+    '''Represents an intersection movement
+    with a volume, a type (through, left or right)
+    and an equivalent for movement type'''
+    def __init__(self, volume,  type, mvtEquivalent = 1):
+        self.volume = volume
+        self.type = type
+        self.mvtEquivalent = mvtEquivalent
+
+    def getTVUVolume(self):
+        return self.mvtEquivalent*self.volume.getPCEVolume()    
+
+class IntersectionApproach:
+    def __init__(self, leftTurnVolume, throughVolume, rightTurnVolume):
+        self.leftTurnVolume = leftTurnVolume
+        self.throughVolume = throughVolume
+        self.rightTurnVolume = rightTurnVolume
+
+    def getTVUVolume(self, leftTurnEquivalent = 1, throughEquivalent = 1, rightTurnEquivalent = 1):
+        return self.leftTurnVolume.getPCEVolume()*leftTurnEquivalent+self.throughVolume.getPCEVolume()*throughEquivalent+self.rightTurnVolume.getPCEVolume()*rightTurnEquivalent
+
+class LaneGroup:
+    '''Class that represents a group of mouvements'''
+
+    def __init__(self):
+        self.mouvements = {'left': [],
+                           'through': [],
+                           'right': []}
+
+    # all the add*Mvt should add a IntersectionMovement instance
+    def addLeftMvt(self, vol):
+        self.mouvements['left'].append(vol)
+
+    def addRightMvt(self, vol):
+        self.mouvements['right'].append(vol)
+
+    def addThroughMvt(self, vol):
+        self.mouvements['through'].append(vol)
+
+    def getTVUVolume(self, leftTurnEquivalent = 1, throughEquivalent = 1, rightTurnEquivalent = 1):
+        return leftTurnEquivalent*sum([m.getPCEVolume() for m in mouvements['left']])\
+            +rightTurnEquivalent*sum([m.getPCEVolume() for m in mouvements['right']])\
+            +throughTurnEquivalent*sum([m.getPCEVolume() for m in mouvements['through']])
+
+def checkProtectedLeftTurn(leftMvt, opposedThroughMvt):
+    '''Checks if one of the main two conditions on left turn is verified
+    The lane groups should contain left and through movement'''
+    return leftMvt.volume >= 200 or leftMvt.volume*opposedMvt.volume/opposedMvt.nLanes > 50000
+
+def optimalCycle(lostTime, criticalCharge):
+    return ceil((1.5*lostTime+5)/(1-criticalCharge))
+
+def computeInterGreen(perceptionReactionTime, initialSpeed, intersectionLength, vehicleAverageLength = 6, deceleration = 3):
+    '''Computes the intergreen time (yellow/amber plus all red time)
+    Deceleration is positive
+    All variables should be in the same units'''
+    if deceleration > 0:
+        return [perceptionReactionTime+initialSpeed/(2*deceleration), (intersectionLength+vehicleAverageLength)/initialSpeed]
+    else:
+        print 'Issue deceleration should be strictly positive'
+        return None