Index: src/org/openstreetmap/josm/data/validation/OsmValidator.java
===================================================================
--- src/org/openstreetmap/josm/data/validation/OsmValidator.java	(revision 15334)
+++ src/org/openstreetmap/josm/data/validation/OsmValidator.java	(working copy)
@@ -42,6 +42,7 @@
 import org.openstreetmap.josm.data.validation.tests.BarriersEntrances;
 import org.openstreetmap.josm.data.validation.tests.Coastlines;
 import org.openstreetmap.josm.data.validation.tests.ConditionalKeys;
+import org.openstreetmap.josm.data.validation.tests.ConnectivityRelationCheck;
 import org.openstreetmap.josm.data.validation.tests.CrossingWays;
 import org.openstreetmap.josm.data.validation.tests.DuplicateNode;
 import org.openstreetmap.josm.data.validation.tests.DuplicateRelation;
@@ -148,6 +149,8 @@
         LongSegment.class, // 3500 .. 3599
         PublicTransportRouteTest.class, // 3600 .. 3699
         RightAngleBuildingTest.class, // 3700 .. 3799
+        ConnectivityRelationCheck.class, // 3800 .. 3899
+
     };
 
     /**
Index: src/org/openstreetmap/josm/data/validation/tests/ConnectivityRelationCheck.java
===================================================================
--- src/org/openstreetmap/josm/data/validation/tests/ConnectivityRelationCheck.java	(nonexistent)
+++ src/org/openstreetmap/josm/data/validation/tests/ConnectivityRelationCheck.java	(working copy)
@@ -0,0 +1,116 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.data.validation.tests;
+
+import static org.openstreetmap.josm.tools.I18n.tr;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.osm.OsmPrimitiveType;
+import org.openstreetmap.josm.data.osm.Relation;
+import org.openstreetmap.josm.data.osm.RelationMember;
+import org.openstreetmap.josm.data.validation.Severity;
+import org.openstreetmap.josm.data.validation.Test;
+import org.openstreetmap.josm.data.validation.TestError;
+
+/**
+ * Check for inconsistencies in lane information between relation and members.
+ */
+public class ConnectivityRelationCheck extends Test {
+
+    protected static final int INCONSISTENT_LANE_COUNT = 3800;
+
+    protected static final int UNKNOWN_CONNECTIVITY_ROLE = 3801;
+
+    protected static final int NO_CONNECTIVITY_TAG = 3802;
+
+    /**
+    * Constructor
+    */
+    public ConnectivityRelationCheck() {
+        super(tr("Connectivity Relation Check"), tr("Checks that lane count of relation matches with lanes of members"));
+    }
+
+    //Get lane count of members from the 'connectivity' tag
+    private Map<String, Integer> countLanesFromConnTag(Relation r) {
+        Map<String, Integer> laneInfo = new HashMap<String, Integer>();
+        if (r.hasKey("connectivity")) {
+            String connectivityString = r.get("connectivity");
+            laneInfo.put("from", 0);
+            laneInfo.put("to", 0);
+            String roleString = "from";
+            for (char ch : connectivityString.toCharArray()) {
+                if (Character.isDigit(ch)) {
+                    int laneNum = Character.getNumericValue(ch);
+                    if (laneNum > laneInfo.get(roleString)) {
+                        laneInfo.put(roleString, laneNum);
+                    }
+                } else if (ch == ':') {
+                    roleString = "to";
+                } else if (ch == '|') {
+                    roleString = "from";
+                }
+            }
+        }
+        return laneInfo;
+    }
+
+    @Override
+    public void visit(Relation r) {
+        if (r.hasTag("type", "connectivity")) {
+            //No Connectivity, member outside
+            boolean incompleteMember = false, badRole = false;
+            boolean noConnectivityTag = !r.hasKey("connectivity");
+            //Lane count from connectivity tag
+            Map<String, Integer> connTagLanes = countLanesFromConnTag(r);
+            //Lane count from member tags
+            Map<String, Integer> roleLanes = new HashMap<String, Integer>();
+            for (RelationMember rM : r.getMembers()) {
+                if (!incompleteMember) {
+                    incompleteMember = rM.toString().contains("incomplete");
+                }
+                //Check role names
+                String role = rM.getRole();
+                if (!badRole) {
+                    badRole = (!role.equals("from") && !role.equals("to") && !role.equals("via"));
+                }
+                //Check lanes
+                if (rM.getType() == OsmPrimitiveType.WAY) {
+                    OsmPrimitive prim = rM.getMember();
+                    if (prim.hasKey("lanes")) {
+                        if (!rM.getRole().equals("via")) {
+                            roleLanes.put(rM.getRole(), Integer.parseInt(prim.get("lanes")));
+                        }
+                    }
+                }
+            }
+            if (!incompleteMember) {
+                if (noConnectivityTag) {
+                    errors.add(TestError
+                            .builder(this, Severity.WARNING, NO_CONNECTIVITY_TAG)
+                            .message(tr("kaart"), tr("No connectivity tag in connectivity relation"))
+                            .primitives(r)
+                            .build());
+                } else {
+                    boolean fromCheck = roleLanes.get("from") < connTagLanes.get("from");
+                    boolean toCheck = roleLanes.get("to") < connTagLanes.get("to");
+                    if (fromCheck || toCheck) {
+                        errors.add(TestError
+                                .builder(this, Severity.WARNING, INCONSISTENT_LANE_COUNT)
+                                .message(tr("kaart"), tr("Inconsistent lane numbering between relation and members"))
+                                .primitives(r)
+                                .build());
+                    }
+                }
+                if (badRole) {
+                    errors.add(TestError
+                            .builder(this, Severity.WARNING, UNKNOWN_CONNECTIVITY_ROLE)
+                            .message(tr("kaart"), tr("Unkown role in connectivity relation"))
+                            .primitives(r)
+                            .build());
+                }
+            }
+        }
+    }
+}