diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f45517..6aa093c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,8 +12,11 @@ All notable changes to this project will be documented in this file.
 [pkjjl]: https://pkgdocs.julialang.org/v1/compatibility/#compat-pre-1.0
 
 # [0.6.0] -- 2022-12-15
-### Changed
-- Switch from Euclidean distance to approximate driving distance
+### Added
+- Allow RELOG to calculate approximate driving distances, instead of just straight-line distances between points.
+
+### Fixed
+- Fix bug that caused building period parameter to be ignored
 
 ## [0.5.2] -- 2022-08-26
 ### Changed
diff --git a/docs/src/format.md b/docs/src/format.md
index 01fdc7d..4164370 100644
--- a/docs/src/format.md
+++ b/docs/src/format.md
@@ -14,6 +14,7 @@ The **parameters** section describes details about the simulation itself.
 |:--------------------------|:---------------|
 |`time horizon (years)`     | Number of years in the simulation.
 |`building period (years)`  | List of years in which we are allowed to open new plants. For example, if this parameter is set to `[1,2,3]`, we can only open plants during the first three years. By default, this equals `[1]`; that is, plants can only be opened during the first year. |
+|`distance metric` | Metric used to compute distances between pairs of locations. Valid options are: `"Euclidean"`, for the straight-line distance between points; or `"driving"` for an approximated driving distance. If not specified, defaults to `"Euclidean"`.
 
 
 #### Example
@@ -21,7 +22,8 @@ The **parameters** section describes details about the simulation itself.
 {
     "parameters": {
         "time horizon (years)": 2,
-        "building period (years)": [1]
+        "building period (years)": [1],
+        "distance metric": "driving",
     }
 }
 ```
@@ -220,6 +222,7 @@ Database | Description | Examples
 * Plants can be expanded at any time, even long after they are open.
 * All material available at the beginning of a time period must be entirely processed by the end of that time period. It is not possible to store unprocessed materials from one time period to the next.
 * Up to two plant sizes are currently supported. Variable operating costs must be the same for all plant sizes.
+* Accurate driving distances are only available for the continental United States.
 
 ## Output Data Format (JSON)
 
diff --git a/instances/s1.json b/instances/s1.json
index e88e8c5..279f1ae 100644
--- a/instances/s1.json
+++ b/instances/s1.json
@@ -1,6 +1,7 @@
 {
     "parameters": {
-        "time horizon (years)": 2
+        "time horizon (years)": 2,
+        "distance metric": "driving"
     },
     "products": {
         "P1": {
diff --git a/src/graph/build.jl b/src/graph/build.jl
index 12640d6..418ac5e 100644
--- a/src/graph/build.jl
+++ b/src/graph/build.jl
@@ -40,7 +40,6 @@ function build_graph(instance::Instance)::Graph
     end
 
     # Build arcs from collection centers to plants, and from one plant to another
-    metric = _KnnDrivingDistance()
     for source in [collection_shipping_nodes; plant_shipping_nodes]
         for dest in process_nodes_by_input_product[source.product]
             distance = _calculate_distance(
@@ -48,7 +47,7 @@ function build_graph(instance::Instance)::Graph
                 source.location.longitude,
                 dest.location.latitude,
                 dest.location.longitude,
-                metric,
+                instance.distance_metric,
             )
             values = Dict("distance" => distance)
             arc = Arc(source, dest, values)
diff --git a/src/graph/dist.jl b/src/graph/dist.jl
index abaecc0..777ad87 100644
--- a/src/graph/dist.jl
+++ b/src/graph/dist.jl
@@ -6,19 +6,12 @@ using Geodesy
 using NearestNeighbors
 using DataFrames
 
-Base.@kwdef mutable struct _KnnDrivingDistance
-    tree = nothing
-    ratios = nothing
-end
-
-mutable struct _EuclideanDistance end
-
 function _calculate_distance(
     source_lat,
     source_lon,
     dest_lat,
     dest_lon,
-    ::_EuclideanDistance,
+    ::EuclideanDistance,
 )::Float64
     x = LLA(source_lat, source_lon, 0.0)
     y = LLA(dest_lat, dest_lon, 0.0)
@@ -30,7 +23,7 @@ function _calculate_distance(
     source_lon,
     dest_lat,
     dest_lon,
-    metric::_KnnDrivingDistance,
+    metric::KnnDrivingDistance,
 )::Float64
     if metric.tree === nothing
         basedir = joinpath(dirname(@__FILE__), "..", "..", "data")
@@ -54,13 +47,8 @@ function _calculate_distance(
     end
 
     # Compute Euclidean distance
-    dist_euclidean = _calculate_distance(
-        source_lat,
-        source_lon,
-        dest_lat,
-        dest_lon,
-        _EuclideanDistance(),
-    )
+    dist_euclidean =
+        _calculate_distance(source_lat, source_lon, dest_lat, dest_lon, EuclideanDistance())
 
     # Predict ratio
     idxs, _ = knn(metric.tree, [source_lat, source_lon, dest_lat, dest_lon], 5)
diff --git a/src/instance/parse.jl b/src/instance/parse.jl
index 5720393..d105aee 100644
--- a/src/instance/parse.jl
+++ b/src/instance/parse.jl
@@ -23,10 +23,23 @@ function parse(json)::Instance
     validate(json, Schema(json_schema))
 
     building_period = [1]
-    if "building period (years)" in keys(json)
-        building_period = json["building period (years)"]
+    if "building period (years)" in keys(json["parameters"])
+        building_period = json["parameters"]["building period (years)"]
     end
 
+    distance_metric = EuclideanDistance()
+    if "distance metric" in keys(json["parameters"])
+        metric_name = json["parameters"]["distance metric"]
+        if metric_name == "driving"
+            distance_metric = KnnDrivingDistance()
+        elseif metric_name == "Euclidean"
+            # nop
+        else
+            error("Unknown distance metric: $metric_name")
+        end
+    end
+    @show distance_metric
+
     plants = Plant[]
     products = Product[]
     collection_centers = CollectionCenter[]
@@ -176,5 +189,12 @@ function parse(json)::Instance
     @info @sprintf("%12d collection centers", length(collection_centers))
     @info @sprintf("%12d candidate plant locations", length(plants))
 
-    return Instance(T, products, collection_centers, plants, building_period)
+    return Instance(
+        T,
+        products,
+        collection_centers,
+        plants,
+        building_period,
+        distance_metric,
+    )
 end
diff --git a/src/instance/structs.jl b/src/instance/structs.jl
index 190ae9b..692fbca 100644
--- a/src/instance/structs.jl
+++ b/src/instance/structs.jl
@@ -48,10 +48,21 @@ mutable struct Plant
     storage_cost::Vector{Float64}
 end
 
+
+abstract type DistanceMetric end
+
+Base.@kwdef mutable struct KnnDrivingDistance <: DistanceMetric
+    tree = nothing
+    ratios = nothing
+end
+
+mutable struct EuclideanDistance <: DistanceMetric end
+
 mutable struct Instance
     time::Int64
     products::Vector{Product}
     collection_centers::Vector{CollectionCenter}
     plants::Vector{Plant}
     building_period::Vector{Int64}
+    distance_metric::DistanceMetric
 end
diff --git a/src/schemas/input.json b/src/schemas/input.json
index fd46ec0..1cafb71 100644
--- a/src/schemas/input.json
+++ b/src/schemas/input.json
@@ -14,6 +14,9 @@
             "properties": {
                 "time horizon (years)": {
                     "type": "number"
+                },
+                "distance metric": {
+                    "type": "string"
                 }
             },
             "required": [
diff --git a/test/graph/dist_test.jl b/test/graph/dist_test.jl
index cce8b6a..d643602 100644
--- a/test/graph/dist_test.jl
+++ b/test/graph/dist_test.jl
@@ -11,7 +11,7 @@ using RELOG
         -87.656,
         39.764,
         -86.148,
-        RELOG._EuclideanDistance(),
+        RELOG.EuclideanDistance(),
     ) == 265.818
 
     # Approximate driving distance between Chicago and Indianapolis
@@ -20,6 +20,6 @@ using RELOG
         -87.656,
         39.764,
         -86.148,
-        RELOG._KnnDrivingDistance(),
+        RELOG.KnnDrivingDistance(),
     ) == 316.43
 end