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+Environmental considerations (penalties for traffic, noise, town, no river, no forest) are possible due to the creation of pseudo tags during processing OSM data by spatial SQL queries in https://github.com/abrensch/brouter/blob/master/misc/scripts/mapcreation/brouter.sql. During this processing, roads are extended by a 32 m buffer creating 64 m wide lines. Then it is calculated what percentage of such line is at a specific distance to a noise source or within a forest, for example. The percentage is converted to a factor and the factor is assigned to a class. Ways that pass through different environments and are represented by a single OSM way can be problematic because the class is always based on the average environment along an entire OSM way. For traffic, calculations are on another level of complexity.
+
+### consider_noise, noise_penalty
+For proximity of noisy roads (secondary and higher). The noise factor represents the proportion of a road's buffer area that lies within the 64-meter buffer of noisy roads. This proportion is reduced: 
+- for motorways and trunk roads with max speed < 105 by 1.5
+- for primary roads 2 times 
+- 3 times if maxspeed is 75 - 105  for primary and secondary
+- other secondary roads 5 times 
+
+Noise class is roughly proportional to the noise factor:
+
+noise_factor = noise class
+- < 0.1             =                            '1'
+- < 0.25            =                          '2'
+- < 0.4              =                           '3'
+- < 0.55               =                        '4'
+- < 0.8                   =                      '5'
+- ELSE                     =                    '6'
+
+To be classified as noise class 6, a way must be less than 13 m on average from the middle of the carriageway of a motorway with a maximum speed exceeding 105. For a class 5, the distance must be up to 35 meters.  (1 - noise factor) * 64 m for a given class determines the distance
+
+**Max noise class:**
+| Max speed | Motorway, trunk |Primary|Secondary   	|
+|---				|:---:						|:---:	|:---:	|
+| >105   		|6  							|4	  	| 3  	|
+| 105				|5		   					|4	   	|3   	|
+| 75		  	|5		   					|3 	  	|2   	|
+
+
+### consider_river, no_river_penalty
+OSM data recognized as river:
+- waterway: river, canal
+- natural: water (except wastewater)
+
+Waterways have 32 m wide buffers. Water areas have 77 m wide buffers.
+
+river_see = river class 
+- < 0.17                  =                  '1'
+- < 0.35                     =                '2'
+- < 0.57                      =              '3'
+- < 0.80                       =             '4'
+- < 0.95                        =            '5'
+- ELSE                            =           '6'
+
+### consider_forest, no_forest_penalty
+OSM data recognized as forest: 
+- landuse: forest, allotments, flowerbed, orchard, vineyard, recreation_ground, village_green
+- leisure: garden, park, nature_reserve
+  
+No forest buffers are used.
+
+Imagine you trace the way with a pencil drawing lines 62 meters wide. Then estimated_forest_class=6 corresponds to the case that at least 98% of the line is in the woodland. This number is called a green factor.
+
+green_factor = forest class
+- < 0.1             =                         NULL
+- < 0.2               =                             '1'
+- < 0.4                 =                           '2'
+- < 0.6 		=          '3'
+- < 0.8                   =                         '4'
+- < 0.98               =                           '5'
+- ELSE                    =                        '6'
+
+
+
+### consider_town, town_penalty 
+Town_class is determined by population data from OSM.
+
+Class
+- 1 = 	50-80 	k people
+- 2 = 80-150 k people
+- 3 =	150 - 400 k people
+- 4 = 400 - 1,000 k people
+- 5 = 1 - 2 million people
+- 6 = > 2 million people
+
+### consider_traffic, traffic_penalty
+(modified copy from the sql file).
+OSM data used to estimate the traffic:
+-    population of towns (+ distance from position to the towns)
+-    size of industrial areas (landuse=industrial) and distance to them. Not considered: solar & wind farms.
+-    airports international
+-    motorway and trunk road density - traffic on motorways decreases traffic on primary/secondary/tertiary. Calculated on a grid (100 km^2)
+-    density of highways (tertiary and higher) calculated on a grid (100 km^2). Traffic decreases when more such roads are available.     Exceptions: near junctions between motorways and other roads the traffic increases on these roads.
+-    mountain-ranges calculated as density of peaks > 400 m traffic is generally on highways in such regions higher as only generated by the local population or industrial areas
+- calculate traffic from the population (for each segment of type primary secondary tertiary)
+- SUM of (population of each town < 100 km) / ( town-radius + 2500 + dist(segment-position to the town) ** 2 )
+-  town-radius is calculated as sqrt(population)