rubyのparallelをselenium webdriverで使いたいがエラーになる

ruby
1require 'selenium-webdriver'
2require 'parallel'
3
4Parallel.each(url_list, in_threads: 4) do |row|
5  @driver = Selenium::WebDriver.for :chrome
6
7  @driver.navigate.to(row)
8  処理
9end

このように実装すると4つのブラウザが立ち上がって、それぞれ別のURLにアクセスするのですが、1つ目の処理を終えるとそれぞれブラウザが閉じてしまい、以下のエラーが表示されます。

C:/Ruby23/lib/ruby/2.3.0/net/protocol.rb:158:in `wait_readable': An operation was attempted on something that is not a socket. (Errno::ENOTSOCK)

        from C:/Ruby23/lib/ruby/2.3.0/net/protocol.rb:158:in `rbuf_fill'
        from C:/Ruby23/lib/ruby/2.3.0/net/protocol.rb:136:in `readuntil'
        from C:/Ruby23/lib/ruby/2.3.0/net/protocol.rb:146:in `readline'
        from C:/Ruby23/lib/ruby/2.3.0/net/http/response.rb:40:in `read_status_line'
        from C:/Ruby23/lib/ruby/2.3.0/net/http/response.rb:29:in `read_new'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:1437:in `block in transport_request'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:1434:in `catch'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:1434:in `transport_request'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:1407:in `request'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:1400:in `block in request'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:853:in `start'
        from C:/Ruby23/lib/ruby/2.3.0/net/http.rb:1398:in `request'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/remote/http/default.rb:124:in `response_for'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/remote/http/default.rb:78:in `request'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/remote/http/common.rb:61:in `call'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/remote/bridge.rb:678:in `raw_execute'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/remote/bridge.rb:656:in `execute'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/remote/bridge.rb:339:in `execute_script'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/selenium-webdriver-3.4.0/lib/selenium/webdriver/common/driver.rb:232:in `execute_script'
        from C:/ruby_study/hoiku_db/hoiku_db.rb:147:in `rescue in block in <main>'
        from C:/ruby_study/hoiku_db/hoiku_db.rb:110:in `block in <main>'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/parallel-1.11.2/lib/parallel.rb:486:in `call_with_index'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/parallel-1.11.2/lib/parallel.rb:342:in `block (2 levels) in work_in_threads'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/parallel-1.11.2/lib/parallel.rb:495:in `with_instrumentation'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/parallel-1.11.2/lib/parallel.rb:341:in `block in work_in_threads'
        from C:/Ruby23/lib/ruby/gems/2.3.0/gems/parallel-1.11.2/lib/parallel.rb:206:in `block (2 levels) in in_threads'

解決策はありますでしょうか？